JUnit：另一种测试异常的模式

Question

我在一个包含许多嵌入错误代码的“BusinessException”的项目中工作。

在每个异常单元测试中，我都必须测试重复这种模式的错误代码：

@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，无法使用JUnit注释）

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();
}

@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“干净”吗？你认为可以改善吗？你觉得它太重和/或没用吗？我的主要目标是在我们的开发团队中统一测试异常。（当然还有因式分解代码）

感谢阅读！

Answer 1

JUnitExpectedException规则怎么样？

首先，在测试类的顶部声明规则:

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

然后，在测试方法中，您可以声明可以期待异常:

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

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

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);
    }
}

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));

如果您有一个公共的接口，它用getErrorCode()方法定义业务异常，例如callErrorAwareException，那么您可以扩展TypeSafeMatcher 类，以创建稍微干净一点的代码：

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而不是纯junit，否则hamcrest类将与junit中包含的hamcrest类冲突。在maven中，如下所示：

<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>