使用junit @Rule，expectCause（）和hamcrest匹配器

问题描述

我有一个测试：

@Rule
public ExpectedException thrown = ExpectedException.none();
...
@Test
public void testMethod()
{
    final String error = "error message";
    Throwable expectedCause = new IllegalStateException(error);
    thrown.expectCause(org.hamcrest.Matchers.<Throwable>equalTo(expectedCause));
    someServiceThatTrowsException.foo();
}

当通过mvn运行测试方法时，我收到错误：

When run via mvn the test method, I'm getting the error:

测试编译正常。

请帮帮我，无法理解如何测试异常的原因？

Please help me, cannot understand how to test the cause of the exception?

推荐答案

以这种方式试试：

@Rule public ExpectedException thrown = ExpectedException.none();

@Test public void testMethod() throws Throwable {
    final String error = "error message";
    Throwable expectedCause = new IllegalStateException(error);
    thrown.expectCause(IsEqual.equalTo(expectedCause));
    throw new RuntimeException(expectedCause);
}

考虑不要通过等号检查原因，而是通过IsInstanceOf和/或comapring检查必要时的异常消息。通过equals比较原因也检查堆栈跟踪，这可能比您想要测试/检查的更多。例如：

Consider not to check against the cause by equals but by IsInstanceOf and / or comapring the exception message if necessary. Comparing the cause by equals check the stacktrace as well, which may be more than you would like to test / check. Like this for example:

@Rule public ExpectedException thrown = ExpectedException.none();

@Test public void testMethod() throws Throwable {
    final String error = "error message";
    thrown.expectCause(IsInstanceOf.<Throwable>instanceOf(IllegalStateException.class));
    thrown.expectMessage(error);
    throw new RuntimeException(new IllegalStateException(error));
}

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