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

Question

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 测试方法运行时，我得到了错误：

java.lang.NoSuchMethodError: org.junit.rules.ExpectedException.expectCause(Lorg/hamcrest/Matcher;)V

测试编译正常。

请帮帮我，不明白如何测试异常原因？

Answer 1

验证 Kotlin 语言抛出异常的消息和原因的示例：

@get:Rule
val exceptionRule: ExpectedException = ExpectedException.none()

@Test
fun `test method`() {
    exceptionRule.expect(NestedServletException::class.java)
    exceptionRule.expectMessage("error msg")
    exceptionRule.expectCause(instanceOf(IllegalStateException::class.java))
    // ...

Answer 2

您可以使用内置匹配器 org.hamcrest.Matchers.instanceOf 和 org.junit.internal.matchers.ThrowableMessageMatcher.hasMessage 完全做到这一点：

import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.instanceOf;
import static org.hamcrest.Matchers.both;
import static org.junit.internal.matchers.ThrowableMessageMatcher.hasMessage;

public class temp {
    @Rule
    public ExpectedException expectedException = ExpectedException.none();

    @Test
    public void youCannotDivideByZero() {
        expectedException.expect(RuntimeException.class);
        expectedException.expectMessage(equalTo("Division exception"));
        expectedException.expectCause(both(hasMessage(equalTo("/ by zero"))).and(instanceOf(ArithmeticException.class)));
        divide(1, 0);
    }

    private float divide(int first, int second) {
        try {
            return first / second;
        } catch(ArithmeticException e) {
            throw new RuntimeException("Division exception", e);
        }
    }
}

Answer 3

总结一下。

使用 JUnit 4（hamcrest 1.3，请注意，JUnit 4 依赖于不包含 org.hamcrest.beans 包的 hamcrest-core）

所以，你需要导入：

<dependency>
  <groupId>org.hamcrest</groupId>
  <artifactId>hamcrest-all</artifactId>
  <version>1.3</version>
  <scope>test</scope>
</dependency>

代码：

import static org.hamcrest.CoreMatchers.*;
import static org.hamcrest.beans.HasPropertyWithValue.hasProperty;

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

@Test
public void testThatThrowsNiceExceptionWithCauseAndMessages(){

  expectedException.expect(RuntimeException.class );
  expectedException.expectMessage("Exception message");                                           
  expectedException.expectCause(
    allOf(
      isA(IllegalStateException.class),
      hasProperty("message", is("Cause message"))
    )
  );

  throw 
    new RuntimeException("Exception message", 
      new IllegalStateException("Cause message"));
}

Answer 4

导入

<dependency>
  <groupId>it.ozimov</groupId>
  <artifactId>java7-hamcrest-matchers</artifactId>
  <version>1.3.0</version>
  <scope>test</scope>
</dependency>

然后：

@Rule
public ExpectedException thrown = ExpectedException.none();
...
@Test
public void testMethod()
{
    final String errorMessage = "error message";
    Class<? extends Throwable> expectedCause = IllegalStateException.class;
    thrown.expectCause(ExpectedException.exceptionWithMessage(expectedCause, errorMessage));
    someServiceThatTrowsException.foo();
}

它也适用于原因的子类型。在其他解决方案中，我观察到它们接受超类型，我认为这是错误的。

消息必须相等或包含在原因的错误消息中。

Answer 5

通常我更喜欢以下结构：

expectedException.expectCause(isA(NullPointerException.class));

Answer 6

hamcrest 的 any(Class) 匹配器运行良好：

@Rule
public ExpectedException thrown = ExpectedException.none();
...
@Test
public void testMethod()
{
    thrown.expect(RuntimeException.class);
    thrown.expectCause(org.hamcrest.Matchers.any(IllegalStateException.class));
}

Answer 7

稍微简单地介绍一下静态导入并检查类和原因异常的消息：

import static org.hamcrest.Matchers.allOf;
import static org.hamcrest.Matchers.hasProperty;
import static org.hamcrest.Matchers.instanceOf;
import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertThat;

@Test
public void testThatThrowsNiceExceptionWithCauseAndMessages(){

     expectedException.expect(RuntimeException.class );
     expectedException.expectMessage("Exception message");                                           
     expectedException.expectCause(allOf(instanceOf(IllegalStateException.class),
                                        hasProperty("message", is("Cause message"))) );

     throw new RuntimeException("Exception message", new IllegalStateException("Cause message"));
}

您甚至可以使用 hasProperty 匹配器来断言嵌套原因或测试“getLocalizedMessage”方法。

Answer 8

JUnit 版本问题。

ExpectedException.expectCause() 自 4.11.

4.10 或更低版本中没有这种方法。

您应该确保您的运行时 JUnit 版本 >= 4.11，与您的编译版本相同。

Answer 9

您可以使用此处所述的自定义匹配器 (http://www.javacodegeeks.com/2014/03/junit-expectedexception-rule-beyond-basics.html) 来测试异常原因。

自定义匹配器

private static class CauseMatcher extends TypeSafeMatcher<Throwable> {

    private final Class<? extends Throwable> type;
    private final String expectedMessage;

    public CauseMatcher(Class<? extends Throwable> type, String expectedMessage) {
        this.type = type;
        this.expectedMessage = expectedMessage;
    }

    @Override
    protected boolean matchesSafely(Throwable item) {
        return item.getClass().isAssignableFrom(type)
                && item.getMessage().contains(expectedMessage);
    }

    @Override
    public void describeTo(Description description) {
        description.appendText("expects type ")
                .appendValue(type)
                .appendText(" and a message ")
                .appendValue(expectedMessage);
    }
}

测试用例

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

@Test
public void verifiesCauseTypeAndAMessage() {
    thrown.expect(RuntimeException.class);
    thrown.expectCause(new CauseMatcher(IllegalStateException.class, "Illegal state"));

    throw new RuntimeException("Runtime exception occurred",
            new IllegalStateException("Illegal state"));
}

Answer 10

试试这个方法：

@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 equals 而是通过 IsInstanceOf 和/或在必要时合并异常消息来检查原因。通过 equals 比较原因也检查堆栈跟踪，这可能比您想要测试/检查的要多。比如这样：

@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));
}