diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index a32f07c..ed65ca0 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,6 +1,12 @@
 repos:
   - repo: local
     hooks:
+      - id: run-tests
+        name: Run tests
+        entry: pipenv run test
+        language: system
+        pass_filenames: false
+
       - id: commitlint
         name: Commitlint
         entry: python -m src.commitlint.cli --file
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 5793352..1378c37 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -2,7 +2,7 @@
 
 ## Install Development Dependencies (Using Pipenv)
 
-All the dependencies are managed by Pipenv. Please install Pipenv on your system first by following the instructions at [https://pipenv.pypa.io/en/latest/installation/](https://pipenv.pypa.io/en/latest/installation/).
+All the dependencies are managed by Pipenv. Please install Pipenv on your system first by following the instructions at [https://pipenv.pypa.io/en/latest/installation.html](https://pipenv.pypa.io/en/latest/installation.html).
 
 Once Pipenv is installed, you can install the development dependencies by running the following command:
 
@@ -17,3 +17,11 @@ To install pre-commit and commit-msg hook for this project, run the following co
 ```bash
 pipenv run install-hooks
 ```
+
+## Run tests
+
+Run the tests using the below command:
+
+```bash
+pipenv run test
+```
diff --git a/Pipfile b/Pipfile
index 7e9b042..5bc4ca0 100644
--- a/Pipfile
+++ b/Pipfile
@@ -13,4 +13,5 @@ pytest-cov = "*"
 [scripts]
 test = "pytest"
 coverage = "pytest --cov=src/ --no-cov-on-fail"
+coverage-html = "pytest --cov=src/ --cov-report=html --no-cov-on-fail"
 install-hooks = "pre-commit install --hook-type pre-commit --hook-type commit-msg"
diff --git a/src/commitlint/cli.py b/src/commitlint/cli.py
index b865d71..f330959 100644
--- a/src/commitlint/cli.py
+++ b/src/commitlint/cli.py
@@ -82,10 +82,10 @@ def main() -> None:
     if success:
         sys.stdout.write(f"{COMMIT_SUCCESSFUL}\n")
         sys.exit(0)
-
-    _show_errors(errors)
-    sys.exit(1)
+    else:
+        _show_errors(errors)
+        sys.exit(1)
 
 
 if __name__ == "__main__":
-    main()
+    main()  # pragma: no cover
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..d884a46
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,98 @@
+# type: ignore
+# pylint: disable=all
+
+from unittest.mock import MagicMock, call, mock_open, patch
+
+from src.commitlint.cli import get_args, main
+from src.commitlint.messages import COMMIT_SUCCESSFUL, INCORRECT_FORMAT_ERROR
+
+
+class TestCLI:
+    @patch(
+        "argparse.ArgumentParser.parse_args",
+        return_value=MagicMock(commit_message="commit message", file=None),
+    )
+    def test__get_args__with_commit_message(self, *_):
+        args = get_args()
+        assert args.commit_message == "commit message"
+        assert args.file is None
+
+    @patch(
+        "argparse.ArgumentParser.parse_args",
+        return_value=MagicMock(commit_message=None, file="path/to/file.txt"),
+    )
+    def test__get_args__with_file(self, *_):
+        args = get_args()
+        assert args.file == "path/to/file.txt"
+        assert args.commit_message is None
+
+    @patch("argparse.ArgumentParser.error")
+    def test__get_args__without_commit_message_and_file(self, mock_error):
+        get_args()
+        mock_error.assert_called_with(
+            "Please provide either a commit message or a file."
+        )
+
+    @patch(
+        "src.commitlint.cli.get_args",
+        return_value=MagicMock(commit_message="feat: valid commit message", file=None),
+    )
+    @patch("sys.stdout.write")
+    @patch("sys.exit")
+    def test__main__valid_commit_message(
+        self,
+        mock_sys_exit,
+        mock_stdout_write,
+        *_,
+    ):
+        main()
+        mock_sys_exit.assert_called_with(0)
+        mock_stdout_write.assert_called_with(f"{COMMIT_SUCCESSFUL}\n")
+
+    @patch(
+        "src.commitlint.cli.get_args",
+        return_value=MagicMock(commit_message="Invalid commit message", file=None),
+    )
+    @patch("sys.stderr.write")
+    @patch("sys.exit")
+    def test__main__invalid_commit_message(
+        self,
+        mock_sys_exit,
+        mock_stderr_write,
+        *_,
+    ):
+        main()
+        mock_sys_exit.assert_called_with(1)
+        mock_stderr_write.assert_has_calls(
+            [call("✖ Found 1 errors.\n\n"), call(f"- {INCORRECT_FORMAT_ERROR}\n\n")]
+        )
+
+    @patch(
+        "src.commitlint.cli.get_args",
+        return_value=MagicMock(file="path/to/file.txt", commit_message=None),
+    )
+    @patch("sys.stdout.write")
+    @patch("sys.exit")
+    @patch("builtins.open", mock_open(read_data="feat: valid commit message"))
+    def test__main__valid_commit_message_from_file(
+        self, mock_sys_exit, mock_stdout_write, *_
+    ):
+        main()
+        mock_sys_exit.assert_called_with(0)
+        mock_stdout_write.assert_called_with(f"{COMMIT_SUCCESSFUL}\n")
+
+    @patch(
+        "src.commitlint.cli.get_args",
+        return_value=MagicMock(file="path/to/file.txt", commit_message=None),
+    )
+    @patch("sys.stderr.write")
+    @patch("sys.exit")
+    @patch("builtins.open", mock_open(read_data="Invalid commit message"))
+    def test__main__invalid_commit_message_from_file(
+        self, mock_sys_exit, mock_stderr_write, *_
+    ):
+        main()
+        mock_sys_exit.assert_called_with(1)
+        mock_stderr_write.assert_has_calls(
+            [call("✖ Found 1 errors.\n\n"), call(f"- {INCORRECT_FORMAT_ERROR}\n\n")]
+        )
diff --git a/tests/test_commitlint/__init__.py b/tests/test_commitlint/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_commitlint/test_check_commit_message.py b/tests/test_commitlint/test_check_commit_message.py
new file mode 100644
index 0000000..6b00fd1
--- /dev/null
+++ b/tests/test_commitlint/test_check_commit_message.py
@@ -0,0 +1,94 @@
+# type: ignore
+# pylint: disable=all
+
+from src.commitlint import check_commit_message
+from src.commitlint.constants import COMMIT_MAX_LENGTH
+from src.commitlint.messages import HEADER_LENGTH_ERROR, INCORRECT_FORMAT_ERROR
+
+
+def test__check_commit_message__header_length_error():
+    commit_message = "feat: " + "a" * (COMMIT_MAX_LENGTH + 1)
+    success, errors = check_commit_message(commit_message)
+    assert success is False
+    assert HEADER_LENGTH_ERROR in errors
+
+
+def test__check_commit_message__header_length_valid():
+    commit_message = "feat: " + "a" * (COMMIT_MAX_LENGTH - 1)
+    success, errors = check_commit_message(commit_message)
+    assert success is False
+    assert HEADER_LENGTH_ERROR in errors
+
+
+def test__check_commit_message__incorrect_format_error():
+    commit_message = "This is an invalid commit message"
+    success, errors = check_commit_message(commit_message)
+    assert success is False
+    assert INCORRECT_FORMAT_ERROR in errors
+
+
+def test__check_commit_message__incorrect_format_error_and_health_length_invalid():
+    commit_message = "Test " + "a" * (COMMIT_MAX_LENGTH + 1)
+    success, errors = check_commit_message(commit_message)
+    assert success is False
+    assert HEADER_LENGTH_ERROR in errors
+    assert INCORRECT_FORMAT_ERROR in errors
+
+
+def test__check_commit_message__valid():
+    commit_message = "feat: add new feature"
+    success, errors = check_commit_message(commit_message)
+    assert success is True
+    assert errors == []
+
+
+def test__check_commit_message__valid_with_scope():
+    commit_message = "feat(scope): add new feature"
+    success, errors = check_commit_message(commit_message)
+    assert success is True
+    assert errors == []
+
+
+def test__check_commit_message__empty_scope_error():
+    commit_message = "feat(): add new feature"
+    success, errors = check_commit_message(commit_message)
+    assert success is False
+    assert INCORRECT_FORMAT_ERROR in errors
+
+
+def test__check_commit_message__valid_with_body():
+    commit_message = "fix(scope): fix a bug\n\nThis is the body of the commit message."
+    success, errors = check_commit_message(commit_message)
+    assert success is True
+    assert errors == []
+
+
+def test__check_commit_message__header_line_error():
+    commit_message = "feat(): add new feature\ntest"
+    success, errors = check_commit_message(commit_message)
+    assert success is False
+    assert INCORRECT_FORMAT_ERROR in errors
+
+
+def test__check_commit_message__with_comments():
+    commit_message = "feat(scope): add new feature\n#this is a comment"
+    success, errors = check_commit_message(commit_message)
+    assert success is True
+    assert errors == []
+
+
+def test__check_commit_message__with_diff():
+    commit_message = (
+        "fix: fixed a bug\n\nthis is body\n"
+        "# ------------------------ >8 ------------------------\nDiff message"
+    )
+    success, errors = check_commit_message(commit_message)
+    assert success is True
+    assert errors == []
+
+
+def test__check_commit_message__ignored():
+    commit_message = "Merge pull request #123"
+    success, errors = check_commit_message(commit_message)
+    assert success is True
+    assert errors == []
diff --git a/tests/test_commitlint/test_is_ingored.py b/tests/test_commitlint/test_is_ingored.py
new file mode 100644
index 0000000..1c2b135
--- /dev/null
+++ b/tests/test_commitlint/test_is_ingored.py
@@ -0,0 +1,34 @@
+# type: ignore
+# pylint: disable=all
+
+import pytest
+
+from src.commitlint.commitlint import is_ignored
+
+
+@pytest.mark.parametrize(
+    "commit_message, expected_result",
+    [
+        ("Merge pull request #123", True),
+        ("Merge feature-branch into production", True),
+        ("Merge branch hotfix-123", True),
+        ("Merge tag release-v2.0.1", True),
+        ('Revert "Undo last commit"', True),
+        ("revert Fix-Typo", True),
+        ("Merged bugfix-789 in master", True),
+        ("Merged PR #987: Update documentation", True),
+        ("Merge remote-tracking branch upstream/develop", True),
+        ("Automatic merge from CI/CD", True),
+        ("Auto-merged feature-branch into staging", True),
+        ("Merge tag v3.5.0", True),
+        ("Merge pull request #456: Feature XYZ", True),
+        ('Revert "Apply security patch"', True),
+        ("Merged PR #321: Bugfix - Resolve issue with login", True),
+        ("Merge my feature", False),
+        ("Add new feature", False),
+        ("feat: this is conventional commit format", False),
+    ],
+)
+def test__is_ignored(commit_message, expected_result):
+    result = is_ignored(commit_message)
+    assert result == expected_result
diff --git a/tests/test_commitlint/test_remove_comments.py b/tests/test_commitlint/test_remove_comments.py
new file mode 100644
index 0000000..31ddef1
--- /dev/null
+++ b/tests/test_commitlint/test_remove_comments.py
@@ -0,0 +1,47 @@
+# type: ignore
+# pylint: disable=all
+
+from src.commitlint.commitlint import remove_comments
+
+
+def test__remove_comments__no_comments():
+    input_msg = "Commit message without comments"
+    expected_output = "Commit message without comments"
+    result = remove_comments(input_msg)
+    assert result == expected_output
+
+
+def test__remove_comments__with_comments():
+    input_msg = "# Comment\nRegular text"
+    expected_output = "Regular text"
+    result = remove_comments(input_msg)
+    assert result == expected_output
+
+
+def test__remove_comments__with_diff_message():
+    input_msg = (
+        "Fix a bug\n"
+        "# ------------------------ >8 ------------------------\n"
+        "Diff message"
+    )
+    expected_output = "Fix a bug"
+    result = remove_comments(input_msg)
+    assert result == expected_output
+
+
+def test__remove_comments__multiple_comments():
+    input_msg = "New feature\n# Comment\n# Another comment"
+    expected_output = "New feature"
+    result = remove_comments(input_msg)
+    assert result == expected_output
+
+
+def test__remove_comments__comments_before_diff():
+    input_msg = (
+        "#Comments\n"
+        "# ------------------------ >8 ------------------------\n"
+        "Diff message"
+    )
+    expected_output = ""
+    result = remove_comments(input_msg)
+    assert result == expected_output