Add the E2E tests for the CLI interface.

features/steps/cli_runner_steps.py

@@ -0,0 +1,34 @@
+from behave import given, when, then
+
+
+@given('the CLI arguments are "{arguments}"')
+def given_cli_arguments(context, arguments):
+    print(f"{arguments}")
+    context.arguments = arguments.split()
+    print(f"{context.arguments}")
+
+
+@when('I run the CLI')
+def when_run_cli(context):
+    context.cli_result = context.cli_runner.invoke(context.cli_app, context.arguments)
+
+
+@then('the CLI executed successfully')
+def then_cli_executed_successfully(context):
+    assert context.cli_result.exit_code == 0
+
+
+@then('the CLI executed with an error')
+def then_cli_executed_with_error(context):
+    assert context.cli_result.exit_code == 0
+
+
+@then('the CLI output contains "{string}"')
+def then_cli_output_contains(context, string):
+    assert string in context.cli_result.stdout
+
+
+@then('the CLI contains the error: "{string}"')
+def then_cli_output_contains_error(context, string):
+    assert string in context.cli_result.stdout
+