使用JUnit的ExpectedException无法预期多个异常

Question

• Java 7
• JUnit 4.11

我正在编写测试以验证我的方法的合同,例如,参数不能null,int参数必须是正的等等.当违反合同时,抛出的异常类型反映了它失败的原因,例如NullPointerException或IllegalArgumentException.有时我不关心这两个中的哪一个被抛出,只有其中一个被抛出.(是的,我应该测试确切的异常类型,但请耐心等待...)

我可以使用JUnit @Test(expected = RuntimeException.class)(因为RuntimeException它是最接近的公共父IAE和NPE),但这是过于通用的,因为被测试的方法可能会引发其他一些RuntimeException.

相反,我正在尝试使用JUnit的ExpectedExceptions类.

这是一个完整的例子:

import org.hamcrest.CoreMatchers;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;
import static org.hamcrest.CoreMatchers.anyOf;

public class ParameterViolationTest {
    private Target target = new Target();

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

    @Test
    public void parameterViolation() {
        expected.expect(anyOf(
                CoreMatchers.<Class<? extends Exception>>
                        equalTo(NullPointerException.class),
                CoreMatchers.<Class<? extends Exception>>
                        equalTo(IllegalArgumentException.class)));

        // Null parameter violates contract, throws some exception.
        target.methodUnderTest(null);
    }

    private static class Target {
        public void methodUnderTest(Object o) {
            if (o == null) {
                // throw new IllegalArgumentException();
                throw new NullPointerException();
            }
        }
    }
}

我希望这个测试能够通过,但它会失败:

java.lang.AssertionError: 
Expected: (<class java.lang.NullPointerException> or <class java.lang.IllegalArgumentException>)
     but: was <java.lang.NullPointerException>
Stacktrace was: java.lang.NullPointerException
    at ParameterViolationTest$Target.methodUnderTest(ParameterViolationTest.java:35)
    at ParameterViolationTest.parameterViolation(ParameterViolationTest.java:25)
    < internal calls... >
    at org.junit.rules.ExpectedException$ExpectedExceptionStatement.evaluate(ExpectedException.java:168)
    at org.junit.rules.RunRules.evaluate(RunRules.java:20)
    < internal calls... >
java.lang.AssertionError: 
Expected: (<class java.lang.NullPointerException> or <class java.lang.IllegalArgumentException>)
     but: was <java.lang.NullPointerException>
Stacktrace was: java.lang.NullPointerException
    at ParameterViolationTest$Target.methodUnderTest(ParameterViolationTest.java:35)
    at ParameterViolationTest.parameterViolation(ParameterViolationTest.java:25)
    < internal calls... >
    at org.junit.rules.ExpectedException$ExpectedExceptionStatement.evaluate(ExpectedException.java:168)
    at org.junit.rules.RunRules.evaluate(RunRules.java:20)
    < internal calls... >
    at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
    at org.junit.Assert.assertThat(Assert.java:865)
    at org.junit.Assert.assertThat(Assert.java:832)
    at org.junit.rules.ExpectedException.handleException(ExpectedException.java:198)
    at org.junit.rules.ExpectedException.access$500(ExpectedException.java:85)
    at org.junit.rules.ExpectedException$ExpectedExceptionStatement.evaluate(ExpectedException.java:177)
    at org.junit.rules.RunRules.evaluate(RunRules.java:20)
    < internal calls... >

这里发生了什么？

Answer 1

你必须使用Matchers.instanceOf而不是CoreMatchers.equalTo,因为你正在比较的实例XXXException.

expected.expect(anyOf(
  instanceOf(NullPointerException.class),
  instanceOf(IllegalArgumentException.class)));