test(_comp_get_first_arg): add unit tests

test/t/unit/Makefile.am

@@ -12,8 +12,9 @@ EXTRA_DIST = \
 	test_unit_expand_tilde_by_ref.py \
 	test_unit_filedir.py \
 	test_unit_find_unique_completion_pair.py \
-	test_unit_get_words.py \
+	test_unit_get_first_arg.py \
 	test_unit_get_cword.py \
+	test_unit_get_words.py \
 	test_unit_initialize.py \
 	test_unit_ip_addresses.py \
 	test_unit_known_hosts_real.py \

test/t/unit/test_unit_get_first_arg.py

@@ -0,0 +1,50 @@
+import pytest
+
+from conftest import assert_bash_exec
+
+
+@pytest.mark.bashcomp(cmd=None)
+class TestUnitGetFirstArg:
+    @pytest.fixture(scope="class")
+    def functions(self, bash):
+        assert_bash_exec(
+            bash,
+            '_comp__test_unit() { local -a "words=$1"; local cword=$2 arg=; shift 2; _comp_get_first_arg "$@" && printf "%s\\n" "$arg"; return 0; }',
+        )
+
+    def test_1(self, bash, functions):
+        assert_bash_exec(bash, "_comp__test_unit '()' 0")
+
+    def test_2(self, bash, functions):
+        output = assert_bash_exec(
+            bash, '_comp__test_unit "(a b)" 2', want_output=None
+        ).strip()
+        assert output == "b"
+
+    def test_3(self, bash, functions):
+        output = assert_bash_exec(
+            bash, '_comp__test_unit "(a bc)" 2', want_output=None
+        ).strip()
+        assert output == "bc"
+
+    def test_4(self, bash, functions):
+        output = assert_bash_exec(
+            bash, '_comp__test_unit "(a b c)" 2', want_output=None
+        ).strip()
+        assert output == "b"
+
+    def test_5(self, bash, functions):
+        """Neither of the current word and the command name should be picked
+        as the first argument"""
+        output = assert_bash_exec(
+            bash, '_comp__test_unit "(a b c)" 1', want_output=None
+        ).strip()
+        assert output == ""
+
+    def test_6(self, bash, functions):
+        """Options starting with - should not be picked as the first
+        argument"""
+        output = assert_bash_exec(
+            bash, '_comp__test_unit "(a -b -c d e)" 4', want_output=None
+        ).strip()
+        assert output == "d"