diff --git a/tests/unit_tests/__init__.py b/tests/unit_tests/__init__.py
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index 0000000..e69de29
diff --git a/tests/unit_tests/test_filehelpfunctions.py b/tests/unit_tests/test_filehelpfunctions.py
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+++ b/tests/unit_tests/test_filehelpfunctions.py
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+"""
+License GPLv3 or higher.
+
+(C) 2026 Created by Maikel Mardjan - https://nocomplexity.com/
+
+This program is free software: you can redistribute it and/or modify it under the terms
+of the GNU General Public License as published by the Free Software Foundation, either
+version 3 of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with this
+program. If not, see <https://www.gnu.org/licenses/>.
+
+Unit tests for the filehelpfunctions module.
+"""
+
+from unittest.mock import patch
+
+from pytest import mark
+
+from codeaudit.filehelpfunctions import collect_python_source_files
+
+_EXCLUDE_DIRS = {"docs", "docker", "dist", "tests"}
+_EXAMPLE_DIR = "example_dir"
+
+
+@mark.xfail(reason="'dirs' in the 'collect_python_source_files' is not used.")
+@mark.parametrize("directory", _EXCLUDE_DIRS)
+def test_excluded_dirs(directory):
+    """Test that excluded directories are not included in the result.
+
+    Test vector:
+        - Directory that is excluded from the search.
+
+    Expected behavior:
+        - Walk through a directory that is excluded from the search.
+        - Verify that the result is an empty list.
+    """
+    with patch("codeaudit.filehelpfunctions.os", autospec=True) as mocked_os:
+        mocked_os.walk.return_value = [(".", [directory], ["example.py"])]
+        result = collect_python_source_files(directory=directory)
+        assert result == []
+
+
+def test_not_file():
+    """Test that non-file entries are not included in the result.
+
+    Test vector:
+        - Directory is not on the excluded list.
+        - Tested file is a non-file entry.
+
+    Expected behavior:
+        - Walk through a directory with a non-file entry.
+        - Verify that the result is an empty list.
+    """
+    with patch("codeaudit.filehelpfunctions.os", autospec=True) as mocked_os:
+        mocked_os.walk.return_value = [(".", [_EXAMPLE_DIR], ["example.py"])]
+        mocked_os.path.isfile.return_value = False
+        result = collect_python_source_files(directory=_EXAMPLE_DIR)
+        assert result == []
+
+
+def test_not_ast_parsable():
+    """Test that non-AST-parsable files are not included in the result.
+
+    Test vector:
+        - Directory is not on the excluded list.
+        - Tested file exists.
+        - Tested file is a non-AST-parsable file.
+
+    Expected behavior:
+        - Walk through a directory with a non-AST-parsable file.
+        - Verify that the result is an empty list.
+    """
+    with (
+        patch("codeaudit.filehelpfunctions.os", autospec=True) as mocked_os,
+        patch(
+            "codeaudit.filehelpfunctions.is_ast_parsable", autospec=True
+        ) as mocked_is_ast,
+    ):
+        mocked_os.walk.return_value = [(".", [_EXAMPLE_DIR], ["example.py"])]
+        mocked_os.path.isfile.return_value = True
+        mocked_is_ast.return_value = False
+        result = collect_python_source_files(directory=_EXAMPLE_DIR)
+        assert result == []
+
+
+def test_proper_python_file():
+    """Test that proper Python files are included in the result.
+
+    Test vector:
+        - Directory is not on the excluded list.
+        - Tested file exists.
+        - Tested file is a proper Python file.
+
+    Expected behavior:
+        - Walk through a directory with a proper Python file.
+        - Verify that the result contains the file path.
+    """
+    with (
+        patch("codeaudit.filehelpfunctions.os", autospec=True) as mocked_os,
+        patch(
+            "codeaudit.filehelpfunctions.is_ast_parsable", autospec=True
+        ) as mocked_is_ast,
+    ):
+        mocked_os.walk.return_value = [(".", [_EXAMPLE_DIR], ["example.py"])]
+        mocked_os.path.isfile.return_value = True
+        mocked_os.path.abspath.return_value = "./example.py"
+        mocked_is_ast.return_value = True
+        result = collect_python_source_files(directory=_EXAMPLE_DIR)
+        assert result == ["./example.py"]
+
+
+def test_file_starts_with_dot():
+    """Test that files starting with a dot are not included in the result.
+
+    Test vector:
+        - Directory is not on the excluded list.
+        - Tested file exists.
+        - Tested file starts with a dot.
+
+    Expected behavior:
+        - Walk through a directory with a file starting with a dot.
+        - Verify that the result is an empty list.
+    """
+    with (
+        patch("codeaudit.filehelpfunctions.os", autospec=True) as mocked_os,
+        patch(
+            "codeaudit.filehelpfunctions.is_ast_parsable", autospec=True
+        ) as mocked_is_ast,
+    ):
+        mocked_os.walk.return_value = [(".", [_EXAMPLE_DIR], [".example.py"])]
+        mocked_os.path.isfile.return_value = True
+        mocked_is_ast.return_value = False
+        result = collect_python_source_files(directory=_EXAMPLE_DIR)
+        assert result == []