def test_pipeline():
    # Generate mock data for testing
    X_train = pd.DataFrame({'age': [25, 30, 35, 40], 'income': [50000, 60000, 70000, 80000])
    y_train = pd.Series([0, 0, 1, 1])

    pipeline = Pipeline([('preprocessing', DataPreprocessor()),  # Set up pipeline
                         ('model', LogisticRegression())])
    pipeline.fit(X_train, y_train)  # Fit pipeline on training data

    # Generate mock data for testing
    X_test = pd.DataFrame({'age': [30, 35, 40, 45], 'income': [55000, 65000, 75000, 85000])
    y_test = pd.Series([0, 0, 1, 1])
    y_pred = pipeline.predict(X_test)  
    accuracy = accuracy_score(y_test, y_pred)  # Evaluate pipeline on test data

    assert accuracy > 0.8, "Error: pipeline accuracy is too low."