Descope less relevant unit tests from unified build variants

Switch to more targeted testing of just crypto oriented tests for the
MbedTLS build and just tests that need the fake platform for the fake
platform build.

This reduces the blowup in execution time from running the cartesian
product of builds x tests and saves about 30% of default work done by
gn_build.sh.

BUILD.gn

@@ -235,7 +235,11 @@ if (current_toolchain != "${dir_pw_toolchain}/default:default") {
     enable_host_gcc_build = enable_default_builds && host_os != "win"
 
     # Enable building chip with gcc & mbedtls.
-    enable_host_gcc_mbedtls_build = enable_default_builds && host_os != "win"
+    enable_host_gcc_mbedtls_build = false
+
+    # Enable limited testing with gcc & mbedtls.
+    enable_host_gcc_mbedtls_crypto_tests =
+        enable_default_builds && host_os != "win"
 
     # Build the chip-cert tool.
     enable_standalone_chip_cert_build =
@@ -349,6 +353,15 @@ if (current_toolchain != "${dir_pw_toolchain}/default:default") {
     builds += [ ":host_gcc_mbedtls" ]
   }
 
+  if (enable_host_gcc_mbedtls_crypto_tests) {
+    chip_build("host_gcc_mbedtls_crypto_tests") {
+      test_group = "//src:crypto_tests"
+      toolchain = "${chip_root}/config/mbedtls/toolchain:${host_os}_${host_cpu}_gcc_mbedtls"
+    }
+
+    builds += [ ":host_gcc_mbedtls_crypto_tests" ]
+  }
+
   if (enable_android_builds) {
     chip_build("android_arm") {
       toolchain = "${build_root}/toolchain/android:android_arm"
@@ -376,6 +389,7 @@ if (current_toolchain != "${dir_pw_toolchain}/default:default") {
 
   if (enable_fake_tests) {
     chip_build("fake_platform") {
+      test_group = "//src:fake_platform_tests"
       toolchain = "${build_root}/toolchain/fake:fake_${host_cpu}_gcc"
     }
 

build/chip/chip_build.gni

@@ -20,11 +20,20 @@ template("chip_build") {
   _build_name = target_name
   _toolchain = invoker.toolchain
 
+  if (defined(invoker.test_group)) {
+    _build_target = invoker.test_group
+    _check_target = get_label_info(invoker.test_group, "dir") + ":" +
+                    get_label_info(invoker.test_group, "name") + "_run"
+  } else {
+    _build_target = ":default"
+    _check_target = ":check"
+  }
+
   group("${_build_name}") {
-    deps = [ ":default(${_toolchain})" ]
+    deps = [ "${_build_target}(${_toolchain})" ]
   }
 
   group("check_${_build_name}") {
-    deps = [ ":check(${_toolchain})" ]
+    deps = [ "${_check_target}(${_toolchain})" ]
   }
 }

build/chip/chip_test_group.gni

@@ -60,8 +60,8 @@ template("chip_test_group") {
     }
   }
 
-  if (chip_link_tests) {
-    group("${_test_group_name}_run") {
+  group("${_test_group_name}_run") {
+    if (chip_link_tests) {
       deps = []
       foreach(_test, invoker.deps) {
         deps += [ get_label_info(_test, "label_no_toolchain") + "_run" ]

src/BUILD.gn

@@ -128,4 +128,12 @@ if (chip_build_tests) {
   chip_test_group("fake_platform_tests") {
     deps = [ "${chip_root}/src/lib/dnssd/platform/tests" ]
   }
+
+  # Tests to run with each Crypto PAL
+  chip_test_group("crypto_tests") {
+    deps = [
+      "${chip_root}/src/crypto/tests",
+      "${chip_root}/src/credentials/tests",
+    ]
+  }
 }