JUnit:另一种测试异常的模式

Question

我在一个项目中工作,其中包含许多嵌入了errorCode的"BusinessException".

在每个单元测试异常中,我必须测试这些错误代码重复这种模式:

@Test
public void zipFileReaderCtorShouldThrowAnExceptionWithInexistingArchive() {
    try {
        zfr = new ZipFileReader("unexpected/path/to/file");
        fail("'BusinessZipException' not throwed");
    } catch (BusinessZipException e) {
        assertThat("Unexpected error code", e.getErrorCode(), is(ErrorCode.FILE_NOT_FOUND));
    } catch (Exception e) {
        fail("Unexpected Exception: '" + e + "', expected: 'BusinessZipException'");
    }
}

(由于错误代码测试,使用JUnit注释是不可能的)

我很无聊,特别是因为我必须在fail()的错误消息中复制/粘贴异常名称.

所以,我写了一个Util类.我使用抽象类来处理异常断言测试.

public abstract class TestExceptionUtil {
    public  void runAndExpectException(Class expectedException, String expectedErrorCode) {
        String failUnexpectedExceptionMessage = "Unexpected exception. Expected is: '%s', but got: '%s'";
        try {
            codeToExecute();
            fail("'" + expectedException.getName() + "' not throwed");
        } catch (BusinessException e) {
            if (e.getClass().equals(expectedException)) {
                assertThat("Exception error code not expected", e.getErrorCode(), is(expectedErrorCode));
            } else {
                fail(String.format(failUnexpectedExceptionMessage, expectedException.getName(), e));
            }
        } catch (Exception e) {
            fail(String.format(failUnexpectedExceptionMessage, expectedException.getName(), e));
        }
    }

    abstract public void codeToExecute();
}

然后,客户端以这种方式使用它:

@Test
public void zipFileReaderCtorShouldThrowAnExceptionWithInexistingArchive() {
    new TestExceptionUtil() {
        @Override
        public void codeToExecute() {
            zfr = new ZipFileReader("unexpected/path/to/file");
        }
    }.runAndExpectException(BusinessTechnicalException.class, ErrorCode.FILE_NOT_FOUND);
}

你觉得它"干净"吗？你认为它可以改善吗？你认为它太沉重和/或没用吗？我的主要目标是在开发团队中统一测试异常.(当然还有代码化代码)

谢谢阅读!

Answer 1

JUnit 怎么样？ExpectedException Rule

首先,您Rule在测试类的顶部声明:

@Rule
public final ExpectedException ee = ExpectedException.none();

然后在您的测试方法中,您可以声明您可以期望Exception:

@Test
public void testStuff() {
    ee.expect(IllegalArgumentException.class);
    ee.expectMessage("My Exception text");
}

我认为这比你的方法更清晰.

然后,您可以使用hamcrest Matcher来匹配Exception消息:

@Test
public void testStuff() {
    ee.expect(IllegalArgumentException.class);
    ee.expectMessage(containsString("error"));
    ee.expect(hasProperty("errorCode", is(7)));
}

该hasProperty Matcher会寻找已命名的属性getter和检查它的第二个参数匹配-这是另一种Matcher.

你甚至可以实现自己的Matcher,在这种情况下你不需要依赖hamcrest:

public class ErrorCodeMatcher extends BaseMatcher<Throwable> {

    private final int expectedErrorCode;

    public ErrorCodeMatcher(int expectedErrorCode) {
        this.expectedErrorCode = expectedErrorCode;
    }

    @Override
    public boolean matches(Object o) {
        return ((BusinessZipException) o).getErrorCode() == expectedErrorCode;
    }

    @Override
    public void describeTo(Description d) {
        d.appendText("Expected error code was" + expectedErrorCode);
    }
}

这将使用如下:

ee.expect(new ErrorCodeMatcher(7));

使用static工厂方法和static导入,这可以变得非常干净:

ee.expect(exceptionWithErrorCode(7));

如果您有一个使用方法interface定义业务的公共事件,比如调用那么您可以扩展该类以创建稍微更清晰的代码:ExceptiongetErrorCode()ErrorAwareExceptionTypeSafeMatcher<T>

public class ErrorCodeMatcher<T extends Exception & ErrorAwareException> extends TypeSafeMatcher<T> {

    public static <E extends Exception & ErrorAwareException> ErrorCodeMatcher<E> exceptionWithErrorCode(final int expectedErrorCode) {
        return new ErrorCodeMatcher<E>(expectedErrorCode);
    }
    private final int expectedErrorCode;

    public ErrorCodeMatcher(int expectedErrorCode) {
        this.expectedErrorCode = expectedErrorCode;
    }

    @Override
    protected boolean matchesSafely(final T t) {
        return t.getErrorCode() == expectedErrorCode;
    }

    @Override
    public void describeTo(Description d) {
        d.appendText("Expected error code was" + expectedErrorCode);
    }
}

请注意,如果您确实选择使用hamcrest,那么请确保在项目中包含junit-dep而不是pure junit,否则hamcrest类将与包含的hamcrest类冲突junit.在maven中,这看起来像这样:

<dependency>
    <groupId>org.hamcrest</groupId>
    <artifactId>hamcrest-all</artifactId>
    <version>1.3</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit-dep</artifactId>
    <version>4.11</version>
    <scope>test</scope> 
</dependency>