1. Overview

1.概述

In this tutorial, we’ll explore how to use JUnit fail assertion for common testing scenarios.

在本教程中，我们将探讨如何将JUnit fail断言用于常见的测试场景。

We’ll also see fail() method differences between JUnit 4 and JUnit 5.

我们还将看到 fail() 方法在JUnit 4和JUnit 5之间的差异。

2. Using fail Assertion

2.使用fail断言

The fail assertion fails a test throwing an AssertionError unconditionally.

fail断言使测试失败，无条件地抛出一个AssertionError。

When writing unit tests, we can use fail to explicitly create a failure under desired testing conditions. Let’s see some cases where this can be helpful.

在编写单元测试时，我们可以使用fail来明确地在所需的测试条件下创建一个失败。让我们看看在哪些情况下这是有用的。

2.1. Incomplete Test

2.1.不完整的测试

We can fail a test when it is incomplete or not yet implemented:

当一个测试不完整或尚未实施时，我们可以不通过该测试。

@Test
public void incompleteTest() {
    fail("Not yet implemented");
}

2.2. Expected Exception

2.2.预期的例外情况

We can also do it when we think an exception will happen:

当我们认为会发生异常时，我们也可以这样做。

@Test
public void expectedException() {
    try {
        methodThrowsException();
        fail("Expected exception was not thrown");
    } catch (Exception e) {
        assertNotNull(e);
    }
}

2.3. Unexpected Exception

2.3.意外的例外情况

Failing the test when an exception is not expected to be thrown is another option:

当没有预期的异常被抛出时，失败的测试是另一种选择。

@Test
public void unexpectedException() {
    try {
        safeMethod();
        // more testing code
    } catch (Exception e) {
        fail("Unexpected exception was thrown");
    }
}

2.4. Testing Condition

2.4.测试条件

We can call fail() when a result doesn’t meet some desired condition:

当一个结果不符合某些预期条件时，我们可以调用fail() 。

@Test
public void testingCondition() {
    int result = randomInteger();
    if(result > Integer.MAX_VALUE) {
        fail("Result cannot exceed integer max value");
    }
    // more testing code
}

2.5. Returning Before

2.5.返回之前

Finally, we can fail a test when the code doesn’t return/break when expected:

最后，当代码没有在预期时返回/中断时，我们可以不通过测试。

@Test
public void returnBefore() {
    int value = randomInteger();
    for (int i = 0; i < 5; i++) {
        // returns when (value + i) is an even number
        if ((i + value) % 2 == 0) {
            return;
        }
    }
    fail("Should have returned before");
}

3. JUnit 5 vs JUnit 4

3.JUnit 5 vs JUnit 4

All assertions in JUnit 4 are part of org.junit.Assert class. For JUnit 5 these were moved to org.junit.jupiter.api.Assertions.

JUnit 4中的所有断言都是org.junit.Assert类的一部分。对于JUnit 5，这些都被移到org.junit.jupiter.api.Assertions.。

When we call fail in JUnit 5 and get an exception, we receive an AssertionFailedError instead of AssertionError found in JUnit 4.

当我们在JUnit 5中调用fail并得到一个异常时，我们会收到一个AssertionFailedError，而不是在JUnit 4中发现的AssertionError。

Along with fail() and fail(String message), JUnit 5 includes some useful overloads:

除了fail()和fail(String message)之外，JUnit 5还包括一些有用的重载。

fail(Throwable cause)
fail(String message, Throwable cause)
fail(Supplier<String> messageSupplier)

In addition, all forms of fail are declared as public static <V> V fail() in JUnit 5. The generic return type V, allows these methods to be used as single-statement in lambda expressions:

此外，fail的所有形式在JUnit 5中被声明为public static <V> V fail()。通用的返回类型V,允许这些方法在lambda表达式中作为单句使用：。

Stream.of().map(entry -> fail("should not be called"));

4. Conclusion

4.总结

In this article, we covered some practical use cases for the fail assertion in JUnit. See JUnit Assertions for all available assertions in JUnit 4 and JUnit 5.

在这篇文章中，我们介绍了JUnit中fail断言的一些实际使用案例。请参阅JUnit 断言，了解JUnit 4 和 JUnit 5 中的所有可用断言。

We also highlighted the main differences between JUnit 4 and JUnit 5, and some useful enhancements of the fail method.

我们还强调了JUnit 4和JUnit 5之间的主要区别，以及fail方法的一些有用的改进。

As always, the full source code of the article is available over on GitHub.

一如既往，文章的完整源代码可在GitHub上获得。