diff --git a/.gitignore b/.gitignore
index 1d5ba4c2..e7308766 100644
--- a/.gitignore
+++ b/.gitignore
@@ -40,3 +40,4 @@ hardware.svg
 abc.history
 temp-*
 .run.sh
+,coverage.*
\ No newline at end of file
diff --git a/.vscode/launch.json b/.vscode/launch.json
index 809ee6af..3680f650 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -300,7 +300,7 @@
             "module": "pytest",
             "args": [
                 "-s",
-                "test/commands/test_build.py"
+                "test/test_scons_util.py::test_make_verilator_config_builder"
             ],
             "console": "integratedTerminal",
             "justMyCode": false,
diff --git a/DEVELOPERS.md b/DEVELOPERS.md
index a0a0dd6a..6347a77e 100644
--- a/DEVELOPERS.md
+++ b/DEVELOPERS.md
@@ -13,7 +13,7 @@ make check
 For complete tests with several python versions run the command below. 
 
 ```shell
-make check_all
+make check-all
 ```
 
 For quick tests that that don't load lengthy packagtes from the internet
@@ -38,7 +38,7 @@ When running any of the commands below, a test coverage is generated in the
 ```
 make test          // Partial coverage by offline tests
 make check         // Full coverage
-make check_all     // Full coverage by the last python env run.
+make check-all     // Full coverage by the last python env run.
 ```
 
 
diff --git a/Makefile b/Makefile
index 2f208e20..202d9caf 100644
--- a/Makefile
+++ b/Makefile
@@ -1,57 +1,94 @@
 .PHONY: deps cenv env lint test presubmit publish_test publish install
 
+# NOTE: Some targets have a shortcuts or alias names that are listed on the same line.
+#       The are provided for convinience or for backward competibility. For example
+#       'check-all' has the aliases 'check_all' and 'ca'.
+
 # Install dependencies for apio development
+#
+# Usage:
+#     make deps
 deps:
 	python -m pip install --upgrade pip
 	pip install flit black flake8 pylint tox pytest semantic-version pyserial importlib-metadata
 	
 
 # Create the virtual-environment and update dependencies
+# 
+# Usage:
+#     make cenv
 cenv:  
 	python3 -m venv venv
 	python3 -m venv venv --upgrade
 
-
+# Usage
+#     make env
 env:
 	@echo "For entering the virtual-environment just type:"
 	@echo ". venv/bin/activate"
 
 
 # Lint only, no tests. 
-lint:
+#
+# Usage:
+#     make lint
+#     make l
+lint l:
 	python -m tox -e lint
 
 
 # Offline tests only, no lint, single python version, skipping online tests.
 # This is a partial but fast test.
-test:	
+#
+# Usage:
+#     make test
+#     make t
+test t:	
 	python -m tox --skip-missing-interpreters false -e py312 -- --offline
 
 
 # Tests and lint, single python version, all tests including online..
 # This is a thorough but slow test and sufficient for testign before 
 # commiting changes run this before submitting code.
- check:	
+#
+# Usage:
+#     make check
+#     make c
+check c:	
 	python -m tox --skip-missing-interpreters false -e lint,py312
 
 
 # Tests and lint, multiple python versions.
 # Should be be run automatically on github.
-check_all:
+#
+# Usage:
+#     make check-all
+#     make check_all   // deprecated, to be deleted.
+#     make ca
+check-all check_all ca:
 	python -m tox --skip-missing-interpreters false
 
 
 # Publish to testPypi
-publish_test:
+#
+# Usage:
+#     make publish-test
+#     make publish_test  // deprecated, to be deleted. 
+publish-test publish_test:
 	flit publish --repository testpypi
 
 
 # Publish to PyPi
+#
+# Usage:
+#     make publish
 publish:
 	python -m flit publish
 
 ## Install the tool locally
+#
+# Usage:
+#     make instll
 install:
 	flit build
 	flit install
-
diff --git a/apio/resources/packages.json b/apio/resources/packages.json
index 58afc98a..7c25552d 100644
--- a/apio/resources/packages.json
+++ b/apio/resources/packages.json
@@ -2,7 +2,7 @@
   "examples": {
     "repository": {
       "name": "apio-examples",
-      "organization": "zapta"
+      "organization": "FPGAwars"
     },
     "release": {
       "tag_name": "%V",
@@ -10,7 +10,7 @@
       "uncompressed_name": "apio-examples-%V",
       "folder_name": "examples",
       "extension": "zip",
-      "url_version": "https://github.com/zapta/apio-examples/raw/master/VERSION"
+      "url_version": "https://github.com/FPGAwars/apio-examples/raw/master/VERSION"
     },
     "description": "Verilog examples",
     "env": {}
diff --git a/apio/scons/__init__.py b/apio/scons/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/apio/scons/ecp5/SConstruct b/apio/scons/ecp5/SConstruct
index 6ac47705..6e37a6ef 100644
--- a/apio/scons/ecp5/SConstruct
+++ b/apio/scons/ecp5/SConstruct
@@ -41,7 +41,6 @@
 import os
 from SCons.Script import (
     Builder,
-    AlwaysBuild,
     GetOption,
     COMMAND_LINE_TARGETS,
     ARGUMENTS,
@@ -50,7 +49,7 @@ from apio.scons.scons_util import (
     TARGET,
     BUILD_DIR,
     SConstructId,
-    is_testbench,
+    has_testbench_name,
     basename,
     is_windows,
     get_constraint_file,
@@ -72,13 +71,13 @@ from apio.scons.scons_util import (
     set_up_cleanup,
 )
 
+# # -- Uncomment for debugging of the scons subprocess using a remote debugger.
+# from apio.scons import scons_util
+# scons_util.wait_for_remote_debugger()
 
 # -- Create the environment
 env = create_construction_env(ARGUMENTS)
 
-# -- Uncomment for debugging of the scons subprocess using a remote debugger.
-# from apio.scons import scons_util
-# scons_util.wait_for_remote_debugger(env)
 
 # -- Get arguments.
 FPGA_SIZE = arg_str(env, "fpga_size", "")
@@ -189,11 +188,11 @@ bin_target = env.Bin(TARGET, pnr_target)
 build_target = env.Alias("build", bin_target)
 
 if VERBOSE_YOSYS:
-    AlwaysBuild(synth_target)
+    env.AlwaysBuild(synth_target)
 if VERBOSE_PNR:
-    AlwaysBuild(pnr_target)
+    env.AlwaysBuild(pnr_target)
 if VERBOSE_ALL:
-    AlwaysBuild(synth_target, pnr_target, build_target)
+    env.AlwaysBuild(synth_target, pnr_target, build_target)
 
 # -- Apio report.
 # -- Targets.
@@ -202,7 +201,7 @@ report_action = get_report_action(
     env, SConstructId.SCONSTRUCT_ECP5, VERBOSE_PNR
 )
 report_target = env.Alias("report", PNR_REPORT_FILE, report_action)
-AlwaysBuild(report_target)
+env.AlwaysBuild(report_target)
 
 
 # -- Apio upload.
@@ -210,7 +209,7 @@ AlwaysBuild(report_target)
 # -- hardware.bit -> FPGA.
 programmer_cmd = get_programmer_cmd(env)
 upload_target = env.Alias("upload", bin_target, programmer_cmd)
-AlwaysBuild(upload_target)
+env.AlwaysBuild(upload_target)
 
 
 # -- Apio verify.
@@ -240,7 +239,7 @@ def iverilog_tb_generator(source, target, env, for_signature):
     for a given testbench target."""
     # Extract testbench name from target file name.
     testbench_file = str(target[0])
-    assert is_testbench(env, testbench_file), testbench_file
+    assert has_testbench_name(env, testbench_file), testbench_file
     testbench_name = basename(env, testbench_file)
 
     # Construct the command line.
@@ -300,7 +299,7 @@ env.Append(BUILDERS={"VCD": vcd_builder})
 # -- Targets
 # -- (modules).v -> (modules).out
 verify_out_target = env.IVerilogVerify(TARGET, synth_srcs + test_srcs)
-AlwaysBuild(verify_out_target)
+env.AlwaysBuild(verify_out_target)
 verify_target = env.Alias("verify", verify_out_target)
 
 
@@ -308,9 +307,9 @@ verify_target = env.Alias("verify", verify_out_target)
 # -- Targets.
 # -- (modules).v -> hardware.dot -> hardware.svg.
 dot_target = env.DOT(TARGET, synth_srcs)
-AlwaysBuild(dot_target)
+env.AlwaysBuild(dot_target)
 graphviz_target = env.GRAPHVIZ(TARGET, dot_target)
-AlwaysBuild(graphviz_target)
+env.AlwaysBuild(graphviz_target)
 graph_target = env.Alias("graph", graphviz_target)
 
 
@@ -324,7 +323,7 @@ if "sim" in COMMAND_LINE_TARGETS:
     )
     vcd_file_target = env.VCD(sim_out_target)
     waves_target = make_waves_target(env, vcd_file_target, sim_config)
-    AlwaysBuild(waves_target)
+    env.AlwaysBuild(waves_target)
 
 
 # -- Apio test.
@@ -337,9 +336,9 @@ if "test" in COMMAND_LINE_TARGETS:
         test_out_target = env.IVerilogTestbench(
             sim_config.build_testbench_name, sim_config.srcs
         )
-        AlwaysBuild(test_out_target)
+        env.AlwaysBuild(test_out_target)
         test_vcd_target = env.VCD(test_out_target)
-        AlwaysBuild(test_vcd_target)
+        env.AlwaysBuild(test_vcd_target)
         test_target = env.Alias(
             sim_config.build_testbench_name, [test_out_target, test_vcd_target]
         )
@@ -348,7 +347,7 @@ if "test" in COMMAND_LINE_TARGETS:
     # Create a target for the test command that depends on all the test
     # targets.
     tests_target = env.Alias("test", tests_targets)
-    AlwaysBuild(tests_target)
+    env.AlwaysBuild(tests_target)
 
 
 # -- Apio lint.
@@ -395,7 +394,7 @@ lint_config_target = env.VerilatorConfig(TARGET, [])
 lint_out_target = env.Verilator(TARGET, synth_srcs + test_srcs)
 env.Depends(lint_out_target, lint_config_target)
 lint_target = env.Alias("lint", lint_out_target)
-AlwaysBuild(lint_target)
+env.AlwaysBuild(lint_target)
 
 
 # -- Handle the cleanu of the artifact files.
diff --git a/apio/scons/gowin/SConstruct b/apio/scons/gowin/SConstruct
index 5dc73638..0e909ce9 100644
--- a/apio/scons/gowin/SConstruct
+++ b/apio/scons/gowin/SConstruct
@@ -41,7 +41,6 @@
 import os
 from SCons.Script import (
     Builder,
-    AlwaysBuild,
     GetOption,
     COMMAND_LINE_TARGETS,
     ARGUMENTS,
@@ -49,7 +48,7 @@ from SCons.Script import (
 from apio.scons.scons_util import (
     TARGET,
     SConstructId,
-    is_testbench,
+    has_testbench_name,
     basename,
     is_windows,
     get_constraint_file,
@@ -71,13 +70,13 @@ from apio.scons.scons_util import (
     set_up_cleanup,
 )
 
+# # -- Uncomment for debugging of the scons subprocess using a remote debugger.
+# from apio.scons import scons_util
+# scons_util.wait_for_remote_debugger()
 
 # -- Create the environment
 env = create_construction_env(ARGUMENTS)
 
-# -- Uncomment for debugging of the scons subprocess using a remote debugger.
-# from apio.scons import scons_util
-# scons_util.wait_for_remote_debugger(env)
 
 # -- Get arguments.
 FPGA_MODEL = arg_str(env, "fpga_model", "")
@@ -181,11 +180,11 @@ bin_target = env.Bin(TARGET, pnr_target)
 build_target = env.Alias("build", bin_target)
 
 if VERBOSE_YOSYS:
-    AlwaysBuild(synth_target)
+    env.AlwaysBuild(synth_target)
 if VERBOSE_PNR:
-    AlwaysBuild(pnr_target)
+    env.AlwaysBuild(pnr_target)
 if VERBOSE_ALL:
-    AlwaysBuild(synth_target, pnr_target, build_target)
+    env.AlwaysBuild(synth_target, pnr_target, build_target)
 
 # -- Apio report.
 # -- Targets.
@@ -194,7 +193,7 @@ report_action = get_report_action(
     env, SConstructId.SCONSTRUCT_GOWIN, VERBOSE_PNR
 )
 report_target = env.Alias("report", PNR_REPORT_FILE, report_action)
-AlwaysBuild(report_target)
+env.AlwaysBuild(report_target)
 
 
 # -- Apio upload.
@@ -202,7 +201,7 @@ AlwaysBuild(report_target)
 # -- hardware.fs -> FPGA.
 programmer_cmd = get_programmer_cmd(env)
 upload_target = env.Alias("upload", bin_target, programmer_cmd)
-AlwaysBuild(upload_target)
+env.AlwaysBuild(upload_target)
 
 
 # -- Apio verify.
@@ -232,7 +231,7 @@ def iverilog_tb_generator(source, target, env, for_signature):
     for a given testbench target."""
     # Extract testbench name from target file name.
     testbench_file = str(target[0])
-    assert is_testbench(env, testbench_file), testbench_file
+    assert has_testbench_name(env, testbench_file), testbench_file
     testbench_name = basename(env, testbench_file)
 
     # Construct the command line.
@@ -293,7 +292,7 @@ env.Append(BUILDERS={"VCD": vcd_builder})
 # -- Targets
 # -- (modules).v -> (modules).out
 verify_out_target = env.IVerilogVerify(TARGET, synth_srcs + test_srcs)
-AlwaysBuild(verify_out_target)
+env.AlwaysBuild(verify_out_target)
 verify_target = env.Alias("verify", verify_out_target)
 
 
@@ -301,9 +300,9 @@ verify_target = env.Alias("verify", verify_out_target)
 # -- Targets.
 # -- (modules).v -> hardware.dot -> hardware.svg.
 dot_target = env.DOT(TARGET, synth_srcs)
-AlwaysBuild(dot_target)
+env.AlwaysBuild(dot_target)
 graphviz_target = env.GRAPHVIZ(TARGET, dot_target)
-AlwaysBuild(graphviz_target)
+env.AlwaysBuild(graphviz_target)
 graph_target = env.Alias("graph", graphviz_target)
 
 
@@ -317,7 +316,7 @@ if "sim" in COMMAND_LINE_TARGETS:
     )
     vcd_file_target = env.VCD(sim_out_target)
     waves_target = make_waves_target(env, vcd_file_target, sim_config)
-    AlwaysBuild(waves_target)
+    env.AlwaysBuild(waves_target)
 
 
 # -- Apio test.
@@ -330,9 +329,9 @@ if "test" in COMMAND_LINE_TARGETS:
         test_out_target = env.IVerilogTestbench(
             sim_config.build_testbench_name, sim_config.srcs
         )
-        AlwaysBuild(test_out_target)
+        env.AlwaysBuild(test_out_target)
         test_vcd_target = env.VCD(test_out_target)
-        AlwaysBuild(test_vcd_target)
+        env.AlwaysBuild(test_vcd_target)
         test_target = env.Alias(
             sim_config.build_testbench_name, [test_out_target, test_vcd_target]
         )
@@ -341,7 +340,7 @@ if "test" in COMMAND_LINE_TARGETS:
     # Create a target for the test command that depends on all the test
     # targets.
     tests_target = env.Alias("test", tests_targets)
-    AlwaysBuild(tests_target)
+    env.AlwaysBuild(tests_target)
 
 
 # -- Apio lint.
@@ -384,7 +383,7 @@ lint_config_target = env.VerilatorConfig(TARGET, [])
 lint_out_target = env.Verilator(TARGET, synth_srcs + test_srcs)
 env.Depends(lint_out_target, lint_config_target)
 lint_target = env.Alias("lint", lint_out_target)
-AlwaysBuild(lint_target)
+env.AlwaysBuild(lint_target)
 
 
 # -- Handle the cleanu of the artifact files.
diff --git a/apio/scons/ice40/SConstruct b/apio/scons/ice40/SConstruct
index 205e9bdb..bc4bb616 100644
--- a/apio/scons/ice40/SConstruct
+++ b/apio/scons/ice40/SConstruct
@@ -41,7 +41,6 @@
 import os
 from SCons.Script import (
     Builder,
-    AlwaysBuild,
     GetOption,
     COMMAND_LINE_TARGETS,
     ARGUMENTS,
@@ -49,7 +48,7 @@ from SCons.Script import (
 from apio.scons.scons_util import (
     TARGET,
     SConstructId,
-    is_testbench,
+    has_testbench_name,
     basename,
     is_windows,
     get_constraint_file,
@@ -71,13 +70,13 @@ from apio.scons.scons_util import (
     set_up_cleanup,
 )
 
+# # -- Uncomment for debugging of the scons subprocess using a remote debugger.
+# from apio.scons import scons_util
+# scons_util.wait_for_remote_debugger()
 
 # -- Create the environment
 env = create_construction_env(ARGUMENTS)
 
-# -- Uncomment for debugging of the scons subprocess using a remote debugger.
-# from apio.scons import scons_util
-# scons_util.wait_for_remote_debugger(env)
 
 # -- Get arguments.
 FPGA_SIZE = arg_str(env, "fpga_size", "")
@@ -196,11 +195,11 @@ bin_target = env.Bin(TARGET, pnr_target)
 build_target = env.Alias("build", bin_target)
 
 if VERBOSE_YOSYS:
-    AlwaysBuild(synth_target)
+    env.AlwaysBuild(synth_target)
 if VERBOSE_PNR:
-    AlwaysBuild(pnr_target)
+    env.AlwaysBuild(pnr_target)
 if VERBOSE_ALL:
-    AlwaysBuild(synth_target, pnr_target, build_target)
+    env.AlwaysBuild(synth_target, pnr_target, build_target)
 
 # -- Apio report.
 # -- Targets.
@@ -210,7 +209,7 @@ report_action = get_report_action(
     env, SConstructId.SCONSTRUCT_ICE40, VERBOSE_PNR
 )
 report_target = env.Alias("report", PNR_REPORT_FILE, report_action)
-AlwaysBuild(report_target)
+env.AlwaysBuild(report_target)
 
 
 # -- Apio upload.
@@ -218,14 +217,14 @@ AlwaysBuild(report_target)
 # -- hardware.bin -> FPGA.
 programmer_cmd: str = get_programmer_cmd(env)
 upload_target = env.Alias("upload", bin_target, programmer_cmd)
-AlwaysBuild(upload_target)
+env.AlwaysBuild(upload_target)
 
 
 # -- Apio time.
 # -- Targets.
 # -- hardware.asc -> hardware.rpt
 time_rpt_target = env.Time(pnr_target)
-AlwaysBuild(time_rpt_target)
+env.AlwaysBuild(time_rpt_target)
 time_target = env.Alias("time", time_rpt_target)
 
 
@@ -257,7 +256,7 @@ def iverilog_tb_generator(source, target, env, for_signature):
     for a given testbench target."""
     # Extract testbench name from target file name.
     testbench_file = str(target[0])
-    assert is_testbench(env, testbench_file), testbench_file
+    assert has_testbench_name(env, testbench_file), testbench_file
     testbench_name = basename(env, testbench_file)
 
     # Construct the command line.
@@ -318,7 +317,7 @@ env.Append(BUILDERS={"VCD": vcd_builder})
 # -- Targets
 # -- (modules).v -> (modules).out
 verify_out_target = env.IVerilogVerify(TARGET, synth_srcs + test_srcs)
-AlwaysBuild(verify_out_target)
+env.AlwaysBuild(verify_out_target)
 verify_target = env.Alias("verify", verify_out_target)
 
 
@@ -326,9 +325,9 @@ verify_target = env.Alias("verify", verify_out_target)
 # -- Targets.
 # -- (modules).v -> hardware.dot -> hardware.svg.
 dot_target = env.DOT(TARGET, synth_srcs)
-AlwaysBuild(dot_target)
+env.AlwaysBuild(dot_target)
 graphviz_target = env.GRAPHVIZ(TARGET, dot_target)
-AlwaysBuild(graphviz_target)
+env.AlwaysBuild(graphviz_target)
 graph_target = env.Alias("graph", graphviz_target)
 
 
@@ -342,7 +341,7 @@ if "sim" in COMMAND_LINE_TARGETS:
     )
     vcd_file_target = env.VCD(sim_out_target)
     waves_target = make_waves_target(env, vcd_file_target, sim_config)
-    AlwaysBuild(waves_target)
+    env.AlwaysBuild(waves_target)
 
 
 # -- Apio test.
@@ -355,9 +354,9 @@ if "test" in COMMAND_LINE_TARGETS:
         test_out_target = env.IVerilogTestbench(
             sim_config.build_testbench_name, sim_config.srcs
         )
-        AlwaysBuild(test_out_target)
+        env.AlwaysBuild(test_out_target)
         test_vcd_target = env.VCD(test_out_target)
-        AlwaysBuild(test_vcd_target)
+        env.AlwaysBuild(test_vcd_target)
         test_target = env.Alias(
             sim_config.build_testbench_name, [test_out_target, test_vcd_target]
         )
@@ -366,7 +365,7 @@ if "test" in COMMAND_LINE_TARGETS:
     # Create a target for the test command that depends on all the test
     # targets.
     tests_target = env.Alias("test", tests_targets)
-    AlwaysBuild(tests_target)
+    env.AlwaysBuild(tests_target)
 
 
 # -- Apio lint.
@@ -410,7 +409,7 @@ lint_config_target = env.VerilatorConfig(TARGET, [])
 lint_out_target = env.Verilator(TARGET, synth_srcs + test_srcs)
 env.Depends(lint_out_target, lint_config_target)
 lint_target = env.Alias("lint", lint_out_target)
-AlwaysBuild(lint_target)
+env.AlwaysBuild(lint_target)
 
 
 # -- Handle the cleanu of the artifact files.
diff --git a/apio/scons/scons_util.py b/apio/scons/scons_util.py
index 2700434e..55dc6d69 100644
--- a/apio/scons/scons_util.py
+++ b/apio/scons/scons_util.py
@@ -21,17 +21,19 @@
 import re
 from enum import Enum
 import json
-from typing import Dict, Tuple, List, Optional
+from typing import Dict, Tuple, List, Optional, NoReturn
 from dataclasses import dataclass
 import click
 from SCons import Scanner
 from SCons.Node import NodeList
 from SCons.Node.FS import File
 from SCons.Node.Alias import Alias
-from SCons.Script import DefaultEnvironment
 from SCons.Script.SConscript import SConsEnvironment
+from SCons.Script import DefaultEnvironment
 from SCons.Action import FunctionAction, Action
 from SCons.Builder import Builder
+import SCons.Defaults
+
 
 # -- All the build files and other artifcats are created in this this
 # -- subdirectory.
@@ -60,11 +62,13 @@ def map_params(
 ) -> str:
     """A common function construct a command string snippet from a list
     of arguments. The functon does the following:
-     1. If non replace with []
-     2. Drops empty items.
+     1. If params arg is None replace it with []
+     2. Drops empty or white space only items.
      3. Maps the items using the format string which contains exactly one
         placeholder {}.
      4. Joins the items with a white space char.
+
+     For examples, see the unit test at test_scons_util.py.
     """
     # None designates empty list. Avoiding the pylint non safe default warning.
     if params is None:
@@ -87,12 +91,15 @@ def is_verilog_src(env: SConsEnvironment, file_name: str) -> str:
     """Given a file name, determine by its extension if it's a verilog source
     file (testbenches included)."""
     _, ext = os.path.splitext(file_name)
-    return ext == "v"
+    return ext == ".v"
 
 
-def is_testbench(env: SConsEnvironment, file_name: str) -> bool:
-    """Given a file name, return true if it's a testbench file."""
-    name = basename(env, file_name)
+def has_testbench_name(env: SConsEnvironment, file_name: str) -> bool:
+    """Given a file name, return true if it's base name indicates a
+    testbench. It can be for example abc_tb.v or _build/abc_tb.out.
+    The file extension is ignored.
+    """
+    name, _ = os.path.splitext(file_name)
     return name.lower().endswith("_tb")
 
 
@@ -106,7 +113,20 @@ def is_windows(env: SConsEnvironment) -> bool:
 
 def create_construction_env(args: Dict[str, str]) -> SConsEnvironment:
     """Creates a scons env. Should be called very early in SConstruct.py"""
-    # Create the default env.
+
+    # -- Make sure that the default environment doesn't exist, to make sure
+    # -- we create a fresh environment. This is important with pytest which
+    # -- can run multiple tests in the same python process.
+    # --
+    # pylint: disable=protected-access
+    assert (
+        SCons.Defaults._default_env is None
+    ), "DefaultEnvironment already exists"
+    # pylint: enable=protected-access
+
+    # Create the env. We don't use the DefaultEnvironment (a singleton) to
+    # allow the creation in pytest multiple test environments in the same
+    # tesing process.
     env: SConsEnvironment = DefaultEnvironment(ENV=os.environ, tools=[])
 
     # Add the args dictionary as a new ARGUMENTS var.
@@ -116,12 +136,9 @@ def create_construction_env(args: Dict[str, str]) -> SConsEnvironment:
     # Evaluate the optional force_color arg and set its value
     # an env var on its own.
     assert env.get("FORCE_COLORS") is None
-    env.Replace(FORCE_COLORS=False)  # Tentative.
+    env.Replace(FORCE_COLORS=False)  # Tentative, so we can call arg_bool.
     flag = arg_bool(env, "force_colors", False)
-    env.Replace(FORCE_COLORS=flag)  # Tentative.
-    if not flag:
-        warning(env, "Not forcing scons text colors.")
-
+    env.Replace(FORCE_COLORS=flag)
     # Set the IS_WINDOWS flag based on the required "platform_id" arg.
     platform_id = arg_str(env, "platform_id", False)
     # Note: this is a programming error, not a user error.
@@ -197,6 +214,9 @@ def force_colors(env: SConsEnvironment) -> bool:
 
 
 def msg(env: SConsEnvironment, text: str, fg: str = None) -> None:
+    """Print a message to the user. Similar to click.secho but with
+    proper color enforcement.
+    """
     click.secho(text, fg=fg, color=force_colors(env))
 
 
@@ -215,7 +235,7 @@ def error(env: SConsEnvironment, text: str) -> None:
     msg(env, f"Error: {text}", fg="red")
 
 
-def fatal_error(env: SConsEnvironment, text: str) -> None:
+def fatal_error(env: SConsEnvironment, text: str) -> NoReturn:
     """Prints a short error message and exit with an error code."""
     error(env, text)
     env.Exit(1)
@@ -265,29 +285,6 @@ def dump_env_vars(env: SConsEnvironment) -> None:
     print("----- Env vars end -------")
 
 
-def get_verilator_warning_params(env: SConsEnvironment) -> str:
-    """Construct from the nowwarn and warn arguments an option list
-    for verilator. These values are specified by the user to the
-    apio lint param.
-
-    To test:  apio lint --warn aaa,bbb  --nowarn ccc,ddd
-    """
-
-    no_warn_list = arg_str(env, "nowarn", "").split(",")
-    warn_list = arg_str(env, "warn", "").split(",")
-    # No warn.
-    result = ""
-    for warn in no_warn_list:
-        if warn != "":
-            result += " -Wno-" + warn
-    # Warn.
-    for warn in warn_list:
-        if warn != "":
-            result += " -Wwarn-" + warn
-
-    return result
-
-
 def get_programmer_cmd(env: SConsEnvironment) -> str:
     """Return the programmer command as derived from the scons "prog" arg."""
 
@@ -311,7 +308,7 @@ def get_programmer_cmd(env: SConsEnvironment) -> str:
     return prog_arg
 
 
-def make_verilog_src_scanner(env: SConsEnvironment) -> Scanner:
+def make_verilog_src_scanner(env: SConsEnvironment) -> Scanner.Base:
     """Creates and returns a scons Scanner object for scanning verilog
     files for dependencies.
     """
@@ -344,6 +341,7 @@ def verilog_src_scanner_func(
             ".v"
         ), f"Not a .v file: {file_node.name}"
         includes_set = set()
+        # If the file doesn't exist, this returns an empty string.
         file_text = file_node.get_text_contents()
         # Get IceStudio includes.
         includes = icestudio_list_re.findall(file_text)
@@ -351,7 +349,7 @@ def verilog_src_scanner_func(
         # Get Standard verilog includes.
         includes = verilog_include_re.findall(file_text)
         includes_set.update(includes)
-        # Get a deterministic list.
+        # Get a deterministic list. (Does it sort by file.name?)
         includes_list = sorted(list(includes_set))
         # For debugging
         # info(env, f"*** {file_node.name} includes {includes_list}")
@@ -461,7 +459,7 @@ def get_source_files(env: SConsEnvironment) -> Tuple[List[str], List[str]]:
     synth_srcs = []
     test_srcs = []
     for file in files:
-        if is_testbench(env, file.name):
+        if has_testbench_name(env, file.name):
             test_srcs.append(file.name)
         else:
             synth_srcs.append(file.name)
@@ -662,6 +660,7 @@ def make_verilator_action(
     return action
 
 
+# pylint: disable=too-many-locals
 def _print_pnr_report(
     env: SConsEnvironment,
     json_txt: str,
@@ -696,6 +695,7 @@ def _print_pnr_report(
     clocks = report["fmax"]
     if len(clocks) > 0:
         for clk_net, vals in clocks.items():
+            # pylint: disable=fixme
             # TODO: Confirm clk name extraction for Gowin.
             # Extract clock name from the net name.
             if script_id == SConstructId.SCONSTRUCT_ECP5:
@@ -738,28 +738,26 @@ def print_pnr_report(
     return Action(print_pnr_report, "Formatting pnr report.")
 
 
-def wait_for_remote_debugger(env: SConsEnvironment):
-    """For developement only. Useful for debugging SConstruct scripts that apio
-    runs as a subprocesses. Call this from the SCconstruct script, run apio
-    from a command line, and then connect with the Visual Studio Code debugger
-    using the launch.json debug target. Can also be used to debug apio itself,
-    without having to create or modify the Visual Studio Code debug targets
-    in launch.json"""
+# Enable for debugging a scons process and call from SConstruct.
+#
+# def wait_for_remote_debugger():
+#     """For developement only. Useful for debugging SConstruct scripts that
+#     apio runs as a subprocesses. Call this from the SCconstruct script, run
+#     apio from a command line, and then connect with the Visual Studio Code
+#     debugger using the launch.json debug target. Can also be used to debug
+#     apio itself, without having to create or modify the Visual Studio Code
+#     debug targets in launch.json"""
 
-    # -- We require this import only when using the debugger.
-    import debugpy
+#     # -- We require this import only when using the debugger.
+#     import debugpy
 
-    # -- 5678 is the default debugger port.
-    port = 5678
-    msg(
-        env,
-        f"Waiting for remote debugger on port localhost:{port}.",
-        fg="magenta",
-    )
-    debugpy.listen(port)
-    msg(env, "Attach with the Visual Studio Code debugger.")
-    debugpy.wait_for_client()
-    msg(env, "Remote debugger is attached.", fg="green")
+#     # -- 5678 is the default debugger port.
+#     port = 5678
+#     print(f"Waiting for remote debugger on port localhost:{port}.")
+#     debugpy.listen(port)
+#     print("Attach with the Visual Studio Code debugger.")
+#     debugpy.wait_for_client()
+#     print("Remote debugger is attached.")
 
 
 def set_up_cleanup(env: SConsEnvironment) -> None:
@@ -769,7 +767,7 @@ def set_up_cleanup(env: SConsEnvironment) -> None:
 
     # -- Should be called only when the 'clean' target is specified.
     # -- If this fails, this is a programming error and not a user error.
-    assert env.GetOption("clean")
+    assert env.GetOption("clean"), "Option 'clean' is missing."
 
     # -- Get the list of all files to clean. Scons adds to the list non
     # -- existing files from other targets it encountered.
@@ -780,6 +778,7 @@ def set_up_cleanup(env: SConsEnvironment) -> None:
         + env.Glob("_build")
     )
 
+    # pylint: disable=fixme
     # -- TODO: Remove the cleanup of legacy files after releasing the first
     # -- release with the _build directory.
     # --
@@ -801,10 +800,7 @@ def set_up_cleanup(env: SConsEnvironment) -> None:
         files_to_clean.extend(legacy_files_to_clean)
 
     # -- Create a dummy target.  I
-    dummy_target = env.Command(
-        "no-such-file-1", "no-such-file-2", "no-such-action"
-    )
+    dummy_target = env.Command("cleanup-target", "", "")
 
     # -- Associate all the files with the dummy target.
-    for file in files_to_clean:
-        env.Clean(dummy_target, str(file))
+    env.Clean(dummy_target, files_to_clean)
diff --git a/test/test_scons_util.py b/test/test_scons_util.py
new file mode 100644
index 00000000..ccb8dca2
--- /dev/null
+++ b/test/test_scons_util.py
@@ -0,0 +1,494 @@
+"""
+Tests of scons_util.py
+"""
+
+from os.path import isfile, exists
+from pathlib import Path
+from typing import Dict
+from test.conftest import ApioRunner
+import pytest
+from SCons.Script.SConscript import SConsEnvironment
+import SCons.Script.SConsOptions
+from SCons.Node.FS import FS, File
+import SCons.Node.FS
+import SCons.Environment
+import SCons.Defaults
+import SCons.Script.Main
+from SCons.Script import SetOption
+from pytest import LogCaptureFixture
+from apio.scons.scons_util import (
+    make_verilog_src_scanner,
+    has_testbench_name,
+    is_verilog_src,
+    create_construction_env,
+    get_args,
+    arg_str,
+    arg_bool,
+    is_windows,
+    force_colors,
+    set_up_cleanup,
+    map_params,
+    fatal_error,
+    error,
+    warning,
+    info,
+    msg,
+    get_constraint_file,
+    get_programmer_cmd,
+    make_verilator_config_builder,
+    get_source_files,
+)
+
+DEPENDECIES_TEST_TEXT = """
+// Test file
+parameter v771499 = "v771499.list"
+`include "apio_testing.vh"
+parameter v771499 = "v771499.list"
+`include "apio_testing.v
+"""
+
+
+class SconsHacks:
+    """A collection of staticmethods that encapsulate scons access outside of
+    the official scons API. Hopefully this will not be too difficult to adapt
+    in future versions of SCons."""
+
+    @staticmethod
+    def reset_scons_state() -> None:
+        """Reset the relevant SCons global variables. וUnfurtunally scons
+        uses a few global variables to hold its state. This works well in
+        normal operation where an scons process contains a single scons
+        session but with pytest testing, where multiple independent tests
+        are running in the same process, we need to reset though variables
+        before each test."""
+
+        # -- The Cons.Script.Main.OptionsParser variables contains the command
+        # -- line options of scons. We reset them here and tests can access
+        # -- them using SetOption() and GetOption().
+
+        parser = SCons.Script.SConsOptions.Parser("my_fake_version")
+        values = SCons.Script.SConsOptions.SConsValues(
+            parser.get_default_values()
+        )
+        parser.parse_args(args=[], values=values)
+        SCons.Script.Main.OptionsParser = parser
+
+        # -- Reset the scons target list variable.
+        SCons.Node.FS.default_fs = None
+
+        # -- Clear the SCons targets
+        SCons.Environment.CleanTargets = {}
+
+        # -- Reset the default scons env, if it exists.
+        #
+        # pylint: disable=protected-access
+        SCons.Defaults._default_env = None
+        # pylint: enable=protected-access
+
+    @staticmethod
+    def get_targets() -> Dict:
+        """Get the scons {target -> dependencies} dictionary."""
+        return SCons.Environment.CleanTargets
+
+
+def _make_test_env(
+    args: Dict[str, str] = None, extra_args: Dict[str, str] = None
+) -> SConsEnvironment:
+    """Creates a fresh apio scons env with given args. The env is created
+    with a reference to the current directory.
+    """
+
+    # -- Bring scons to a starting state.
+    SconsHacks.reset_scons_state()
+
+    # -- Default, when we don't really care about the content.
+    if args is None:
+        args = {
+            "platform_id": "darwin_arm64",
+        }
+
+    # -- If specified, overite/add extra args.
+    if extra_args:
+        args.update(extra_args)
+
+    # -- Use the apio's scons env creation function.
+    env = create_construction_env(args)
+
+    return env
+
+
+def test_dependencies(apio_runner: ApioRunner):
+    """Test the verilog scanner which scans a verilog file and extract
+    reference of files it uses.
+    """
+
+    with apio_runner.in_disposable_temp_dir():
+
+        # -- Write a test file name in the current directory.
+        with open("test_file.v", "w", encoding="utf-8") as f:
+            f.write(DEPENDECIES_TEST_TEXT)
+
+        # -- Create a scanner
+        env = _make_test_env()
+        scanner = make_verilog_src_scanner(env)
+
+        # -- Run the scanner. It returns a list of File.
+        file = FS.File(FS(), "test_file.v")
+        dependency_files = scanner.function(file, env, None)
+
+        # -- Create a list with file name strings.
+        file_names = []
+        for f in dependency_files:
+            assert isinstance(f, File)
+            file_names.append(f.name)
+
+        # -- Check the list. The scanner returns the files sorted and
+        # -- with dulicates removed.
+        assert file_names == ["apio_testing.vh", "v771499.list"]
+
+
+def test_has_testbench_name():
+    """Tests the scons_util.test_is_testbench() function"""
+
+    env = _make_test_env
+
+    # -- Testbench names
+    assert has_testbench_name(env, "aaa_tb.v")
+    assert has_testbench_name(env, "aaa_tb.out")
+    assert has_testbench_name(env, "bbb/aaa_tb.v")
+    assert has_testbench_name(env, "bbb\\aaa_tb.v")
+    assert has_testbench_name(env, "aaa__tb.v")
+    assert has_testbench_name(env, "Aaa__Tb.v")
+    assert has_testbench_name(env, "bbb/aaa_tb.v")
+    assert has_testbench_name(env, "bbb\\aaa_tb.v")
+
+    # -- Non testbench names.
+    assert not has_testbench_name(env, "aaatb.v")
+    assert not has_testbench_name(env, "aaa.v")
+
+
+def test_is_verilog_src():
+    """Tests the scons_util.is_verilog_src() function"""
+
+    env = _make_test_env()
+
+    # -- Verilog source names
+    assert is_verilog_src(env, "aaa.v")
+    assert is_verilog_src(env, "bbb/aaa.v")
+    assert is_verilog_src(env, "bbb\\aaa.v")
+    assert is_verilog_src(env, "aaatb.v")
+    assert is_verilog_src(env, "aaa_tb.v")
+
+    # -- Non verilog source names.
+    assert not is_verilog_src(env, "aaatb.vv")
+    assert not is_verilog_src(env, "aaatb.V")
+    assert not is_verilog_src(env, "aaa_tb.vh")
+
+
+def test_env_args():
+    """Tests the scons env args retrieval."""
+
+    args = {
+        "platform_id": "my_platform",
+        "AAA": "my_str",
+        "BBB": "False",
+        "CCC": "True",
+    }
+
+    env = _make_test_env(args.copy())
+    result_args = get_args(env)
+    assert result_args == args
+
+    # -- String args
+    assert arg_str(env, "AAA", "") == "my_str"
+    assert arg_str(env, "ZZZ", "") == ""
+    assert arg_str(env, "ZZZ", "abc") == "abc"
+    assert arg_str(env, "ZZZ", None) is None
+
+    # -- Bool args
+    assert not arg_bool(env, "BBB", None)
+    assert arg_bool(env, "CCC", None)
+    assert not arg_bool(env, "ZZZ", False)
+    assert arg_bool(env, "ZZZ", True)
+    assert arg_bool(env, "ZZZ", None) is None
+
+
+def test_env_platform_id():
+    """Tests the env handling of the paltform_id var."""
+
+    # -- Test with a non windows platform id.
+    env = _make_test_env({"platform_id": "darwin_arm64"})
+    assert not is_windows(env)
+
+    # -- Test with a windows platform id.
+    env = _make_test_env({"platform_id": "windows_amd64"})
+    assert is_windows(env)
+
+
+def test_env_forcing_color():
+    """Tests the color forcing functionality of the scons env."""
+
+    # -- Color forcing turned on (apio writes to a terminal)
+    env = _make_test_env(
+        {"force_colors": "True", "platform_id": "darwin_arm64"}
+    )
+    assert force_colors(env)
+
+    # -- Color forcing turned off (apio process is pipped out)
+    env = _make_test_env(
+        {"force_colors": "False", "platform_id": "darwin_arm64"}
+    )
+    assert not force_colors(env)
+
+
+def test_set_up_cleanup_ok(apio_runner: ApioRunner):
+    """Tests the success path of set_up_cleanup()."""
+
+    with apio_runner.in_disposable_temp_dir():
+
+        # -- Create an env with 'clean' option set.
+        env = _make_test_env()
+        SetOption("clean", True)
+
+        # -- Create files that shouldn't be cleaned up.
+        Path("my_source.v")
+        Path("apio.ini")
+
+        # -- Create files that should be cleaned up.
+        Path("zadig.ini").touch()
+        Path("_build").mkdir()
+        Path("_build/aaa").touch()
+        Path("_build/bbb").touch()
+
+        # -- Run the cleanup setup. It's expected to add a single
+        # -- target with the dependencies to clean up.
+        assert len(SconsHacks.get_targets()) == 0
+        set_up_cleanup(env)
+        assert len(SconsHacks.get_targets()) == 1
+
+        # -- Get the target and its dependencies
+        items_list = list(SconsHacks.get_targets().items())
+        target, dependencies = items_list[0]
+
+        # -- Verify the tartget name, hard coded in set_up_cleanup()
+        assert target.name == "cleanup-target"
+
+        # -- Verif the dependencies. These are the files to delete.
+        file_names = [x.name for x in dependencies]
+        assert file_names == ["aaa", "bbb", "zadig.ini", "_build"]
+
+
+def test_set_up_cleanup_errors():
+    """Tests the error conditions of the set_up_cleanup() function."""
+
+    env = _make_test_env()
+
+    # -- Try without the option 'clean'. It should fail.
+    with pytest.raises(AssertionError) as e:
+        set_up_cleanup(env)
+    assert "Option 'clean' is missing" in str(e)
+
+    # -- Try with the option 'clean'=false. It should fail.
+    SetOption("clean", False)
+    with pytest.raises(AssertionError) as e:
+        set_up_cleanup(env)
+    assert "Option 'clean' is missing" in str(e)
+
+
+def test_map_params():
+    """Test the map_params() function."""
+
+    env = _make_test_env()
+
+    # -- Empty cases
+    assert map_params(env, [], "x_{}_y") == ""
+    assert map_params(env, ["", "   "], "x_{}_y") == ""
+
+    # -- Non empty cases
+    assert map_params(env, ["a"], "x_{}_y") == "x_a_y"
+    assert map_params(env, [" a "], "x_{}_y") == "x_a_y"
+    assert map_params(env, ["a", "a", "b"], "x_{}_y") == "x_a_y x_a_y x_b_y"
+
+
+def test_log_functions(capsys: LogCaptureFixture):
+    """Tests the fatal_error() function."""
+
+    # -- Create the scons env.
+    env = _make_test_env()
+
+    # -- Test msg()
+    msg(env, "My msg")
+    captured = capsys.readouterr()
+    assert "My msg\n" == captured.out
+
+    # -- Test info()
+    info(env, "My info")
+    captured = capsys.readouterr()
+    assert "Info: My info\n" == captured.out
+
+    # -- Test warning()
+    warning(env, "My warning")
+    captured = capsys.readouterr()
+    assert "Warning: My warning\n" == captured.out
+
+    # -- Test error()
+    error(env, "My error")
+    captured = capsys.readouterr()
+    assert "Error: My error\n" == captured.out
+
+    # -- Test fatal_error()
+    with pytest.raises(SystemExit) as e:
+        fatal_error(env, "My fatal error")
+    assert e.value.code == 1
+    captured = capsys.readouterr()
+    assert "Error: My fatal error\n" == captured.out
+
+
+def test_force_colors(capsys: LogCaptureFixture):
+    """Tests that the "force_colors" controls text coloring."""
+    # -- Creating an env without force_colors defaul to false.
+    env = _make_test_env()
+    assert not force_colors(env)
+
+    # -- Output a message and verify no ansi colors.
+    capsys.readouterr()  # clear
+    msg(env, "xyz", fg="red")
+    captured = capsys.readouterr()
+    assert captured.out == "xyz\n"
+
+    # -- Output a message and verify no ansi colors.
+    env = _make_test_env(extra_args={"force_colors": "False"})
+    assert not force_colors(env)
+
+    # -- Output a message and verify text is not colored.
+    capsys.readouterr()  # clear
+    msg(env, "xyz", fg="red")
+    captured = capsys.readouterr()
+    assert captured.out == "xyz\n"
+
+    # -- Creating an env without with force_colors = True
+    env = _make_test_env(extra_args={"force_colors": "True"})
+    assert force_colors(env)
+
+    # -- Output a message and verify text is colored.
+    capsys.readouterr()  # clear
+    msg(env, "xyz", fg="red")
+    captured = capsys.readouterr()
+    assert captured.out == "\x1b[31mxyz\x1b[0m\n"
+
+
+def test_get_constraint_file(
+    capsys: LogCaptureFixture, apio_runner: ApioRunner
+):
+    """Test the get_constraint_file() function."""
+
+    with apio_runner.in_disposable_temp_dir():
+
+        env = _make_test_env()
+
+        # -- If not .pcf files, should assume main name + extension and
+        # -- inform the user about it.
+        capsys.readouterr()  # Reset capture
+        result = get_constraint_file(env, ".pcf", "my_main")
+        captured = capsys.readouterr()
+        assert "assuming 'my_main.pcf'" in captured.out
+        assert result == "my_main.pcf"
+
+        # -- If a single .pcf file, return it.
+        Path("pinout.pcf").touch()
+        result = get_constraint_file(env, ".pcf", "my_main")
+        captured = capsys.readouterr()
+        assert captured.out == ""
+        assert result == "pinout.pcf"
+
+        # -- If thre is more than one, exit with an error message.
+        Path("other.pcf").touch()
+        capsys.readouterr()  # Reset capture
+        with pytest.raises(SystemExit) as e:
+            result = get_constraint_file(env, ".pcf", "my_main")
+        captured = capsys.readouterr()
+        assert e.value.code == 1
+        assert "Error: Found multiple '*.pcf'" in captured.out
+
+
+def test_get_programmer_cmd(capsys: LogCaptureFixture):
+    """Tests the function get_programmer_cmd()."""
+
+    # -- Without a "prog" arg, expected to return "". This is the case
+    # -- when scons handles a command that doesn't use the programmer.
+    env = _make_test_env()
+    assert get_programmer_cmd(env) == ""
+
+    # -- If prog is specified, expected to return it.
+    env = _make_test_env(extra_args={"prog": "my_prog aa $SOURCE bb"})
+    assert get_programmer_cmd(env) == "my_prog aa $SOURCE bb"
+
+    # -- If prog string doesn't contains $SOURCE, expected to exit with an
+    # -- error message.
+    env = _make_test_env(extra_args={"prog": "my_prog aa SOURCE bb"})
+    with pytest.raises(SystemExit) as e:
+        capsys.readouterr()  # Reset capturing.
+        get_programmer_cmd(env)
+    captured = capsys.readouterr()
+    assert e.value.code == 1
+    assert "does not contain the '$SOURCE'" in captured.out
+
+
+def test_make_verilator_config_builder(apio_runner: ApioRunner):
+    """Tests the make_verilator_config_builder() function."""
+
+    with apio_runner.in_disposable_temp_dir():
+
+        # -- Create a test scons env.
+        env = _make_test_env()
+
+        # -- Call the tested function to create a builder.
+        builder = make_verilator_config_builder(env, "test-text")
+
+        # -- Verify builder suffixes.
+        assert builder.suffix == ".vlt"
+        assert builder.src_suffix == []
+
+        # -- Create a target that doesn't exist yet.
+        assert not exists("hardware.vlt")
+        target = FS.File(FS(), "hardware.vlt")
+
+        # -- Invoke the builder's action to create the target.
+        builder.action(target, [], env)
+        assert isfile("hardware.vlt")
+
+        # -- Verify that the the file was created with the tiven text.
+        with open("hardware.vlt", "r", encoding="utf8") as f:
+            text = f.read()
+
+        assert text == "test-text"
+
+
+def test_get_source_files(apio_runner):
+    """Tests the get_source_files() function."""
+
+    with apio_runner.in_disposable_temp_dir():
+
+        # -- Create a test scons env.
+        env = _make_test_env()
+
+        # -- Make files verilog src names (out of order)
+        Path("bbb.v").touch()
+        Path("aaa.v").touch()
+
+        # -- Make files with testbench names (out of order)
+        Path("ccc_tb.v").touch()
+        Path("aaa_tb.v").touch()
+
+        # -- Make files with non related names.
+        Path("ddd.vh").touch()
+        Path("eee.vlt").touch()
+        Path("subdir").mkdir()
+        Path("subdir/eee.v").touch()
+
+        # -- Invoked the tested function.
+        srcs, testbenches = get_source_files(env)
+
+        # -- Verify results.
+        assert srcs == ["aaa.v", "bbb.v"]
+        assert testbenches == ["aaa_tb.v", "ccc_tb.v"]