JUnit - 自定义 Rule

一、自定义 Rule

1、Custom Rule

public class CustomTestRule implements TestRule {

    @Override
    public Statement apply(Statement base, Description description) {
        return new Statement() {

            @Override
            public void evaluate() throws Throwable {
                // 测试执行前
                beforeTest(description);
                try {
                    // 测试执行
                    base.evaluate();
                    // 测试成功
                    onTestSuccess(description);
                } catch (Throwable t) {
                    // 测试失败
                    onTestFailure(description, t);
                    throw t;
                } finally {
                    // 无论测试成功失败
                    afterTest(description);
                }
            }
        };
    }

    private void beforeTest(Description description) {
        System.out.println("开始测试: " + description.getMethodName());
    }

    private void onTestSuccess(Description description) {
        System.out.println("测试通过: " + description.getMethodName());
    }

    private void onTestFailure(Description description, Throwable t) {
        System.out.println("测试失败: " + description.getMethodName() + " - " + t.getMessage());
    }

    private void afterTest(Description description) {
        System.out.println("测试结束: " + description.getMethodName());
    }
}

2、Test

public class CustomTestRuleTest {

    @Rule
    public CustomTestRule customTestRule = new CustomTestRule();

    @Test
    public void test() {
        System.out.println("执行测试逻辑...");
    }
}

# 输出结果

开始测试: test
执行测试逻辑...
测试通过: test
测试结束: test

---

二、实例实操（重试 Rule）

1、Custom Rule

public class RetryRule implements TestRule {

    private final int maxRetries;

    public RetryRule(int maxRetries) {
        this.maxRetries = maxRetries;
    }

    @Override
    public Statement apply(Statement base, Description description) {
        return new Statement() {

            @Override
            public void evaluate() throws Throwable {
                for (int attempt = 1; attempt <= maxRetries; attempt++) {
                    try {
                        System.out.printf("第 %d / %d 次尝试执行测试: %s%n", attempt, maxRetries, description.getMethodName());
                        base.evaluate();
                        System.out.printf("第 %d 次执行测试成功%n", attempt);
                        return;
                    } catch (Throwable e) {
                        System.err.printf("第 %d 次执行测试失败: %s%n", attempt, e.getMessage());
                        if (attempt < maxRetries) {
                            waitBeforeRetry(attempt);
                            continue;
                        }
                        throw e; // 超过最大重试次数，抛出异常
                    }
                }
            }
        };
    }

    private void waitBeforeRetry(int attempt) throws InterruptedException {

        // 指数退避策略
        long waitTime = Math.min(1000 * (long) Math.pow(2, attempt - 1), 10000);
        System.out.printf("等待 %dms 后重试...%n", waitTime);
        Thread.sleep(waitTime);
    }
}

2、Test

public class RetryRuleTest {

    @Rule
    public RetryRule retryRule = new RetryRule(3);

    @Test
    public void test() {
        System.out.println("执行测试逻辑...");
    }
}

# 输出结果

第 1 / 3 次尝试执行测试: test
执行测试逻辑...
第 1 次执行测试成功

public class RetryRuleTest {

    @Rule
    public RetryRule retryRule = new RetryRule(3);

    @Test
    public void test() {
        int a = 10 / 0;
    }
}

# 输出结果

第 1 / 3 次尝试执行测试: test
第 1 次执行测试失败: / by zero
等待 1000ms 后重试...
第 2 / 3 次尝试执行测试: test
第 2 次执行测试失败: / by zero
等待 2000ms 后重试...
第 3 / 3 次尝试执行测试: test
第 3 次执行测试失败: / by zero

---

三、关于异常重新抛出

public class CustomTestRule implements TestRule {

    @Override
    public Statement apply(Statement base, Description description) {
        return new Statement() {

            @Override
            public void evaluate() throws Throwable {
                beforeTest(description);
                try {
                    base.evaluate();
                    onTestSuccess(description);
                } catch (Throwable t) {
                    onTestFailure(description, t);

                    // 异常重新抛出
                    throw t;
                } finally {
                    afterTest(description);
                }
            }
        };
    }

    private void beforeTest(Description description) {
        System.out.println("开始测试: " + description.getMethodName());
    }

    private void onTestSuccess(Description description) {
        System.out.println("测试通过: " + description.getMethodName());
    }

    private void onTestFailure(Description description, Throwable t) {
        System.out.println("测试失败: " + description.getMethodName() + " - " + t.getMessage());
    }

    private void afterTest(Description description) {
        System.out.println("测试结束: " + description.getMethodName());
    }
}

1. 异常重新抛出确保了失败信息能传递到 JUnit 框架，如果不抛出，即使测试方法失败了，也会显示为成功状态

2. TestRule 只是增强测试，而不是替代测试框架的错误处理

3. 异常重新抛出保持测试的原始语义，只是在执行前后添加了额外的逻辑