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，参数不能是null，int参数必须是正数等等。当违反合同时，抛出的异常类型反映失败的原因，例如NullPointerException或IllegalArgumentException。有时我不关心抛出这两个中的哪一个，只是抛出其中一个。（是的，我应正在测试确切的异常类型，但请耐心等待......）

我可以使用JUnit的@Test(expected = RuntimeException.class)（因为RuntimeException是IAE和NPE最近的共同父项，但这是过于通用的，因为被测方法可能会抛出其他一些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，但它失败了：

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

您必须使用Matchers.instanceOf代替CoreMatchers.equalTo，因为您正在比较XXXException的实例。

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

使用JUnit的ExpectedException无法预期多个异常

1 个答案: