处理JUnit中异常的另一种方法：catch-exception

JUnit中有许多处理异常的方法（JUnit中有3种处理异常的方法。选择哪一种呢？ JUnit ExpectedException规则：超越了基础）。在本文中，我将介绍建议尝试的catch-exception库。简而言之， catch-exceptions是一个库，可在一行代码中捕获异常，并使它们可用于进一步分析。

通过Maven安装

为了快速入门，我使用了带有一组测试依赖项（ JUnit，Mocito，Hamcrest，AssertJ ）的单元测试演示项目，并添加了catch-exceptions ：

<dependency><groupId>com.googlecode.catch-exception</groupId><artifactId>catch-exception</artifactId><version>1.2.0</version><scope>test</scope>
</dependency>

因此，依赖关系树如下所示：

[INFO] --- maven-dependency-plugin:2.1:tree @ unit-testing-demo ---
[INFO] com.github.kolorobot:unit-testing-demo:jar:1.0.0-SNAPSHOT
[INFO] +- org.slf4j:slf4j-api:jar:1.5.10:compile
[INFO] +- org.slf4j:jcl-over-slf4j:jar:1.5.10:runtime
[INFO] +- org.slf4j:slf4j-log4j12:jar:1.5.10:runtime
[INFO] +- log4j:log4j:jar:1.2.15:runtime
[INFO] +- junit:junit:jar:4.11:test
[INFO] +- org.mockito:mockito-core:jar:1.9.5:test
[INFO] +- org.assertj:assertj-core:jar:1.5.0:test
[INFO] +- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] +- org.hamcrest:hamcrest-library:jar:1.3:test
[INFO] +- org.objenesis:objenesis:jar:1.3:test
[INFO] \- com.googlecode.catch-exception:catch-exception:jar:1.2.0:test

入门

被测系统（SUT）：

class ExceptionThrower {void someMethod() {throw new RuntimeException("Runtime exception occurred");}void someOtherMethod() {throw new RuntimeException("Runtime exception occurred",new IllegalStateException("Illegal state"));}void yetAnotherMethod(int code) {throw new CustomException(code);}
}

带有AssertJ断言的基本catch-exception BDD样式方法示例：

import org.junit.Test;import static com.googlecode.catchexception.CatchException.*;
import static com.googlecode.catchexception.apis.CatchExceptionAssertJ.*;public class CatchExceptionsTest {@Testpublic void verifiesTypeAndMessage() {when(new SomeClass()).someMethod();then(caughtException()).isInstanceOf(RuntimeException.class).hasMessage("Runtime exception occurred").hasMessageStartingWith("Runtime").hasMessageEndingWith("occured").hasMessageContaining("exception").hasNoCause();               }
}

看起来不错。简洁，可读。没有JUnit运行者。请注意，我指定了我希望引发异常的SomeClass方法。可以想象，我可以在一个测试中检查多个异常。尽管我不推荐这种方法，因为这可能违反了测试的单一责任。

顺便说一句，如果您正在使用Eclipse，这可能对您来说很方便：在Eclipse中创建JUnit测试时，改进具有静态成员类型的内容辅助

查明原因

我认为以下代码无需评论：

import org.junit.Test;import static com.googlecode.catchexception.CatchException.*;
import static com.googlecode.catchexception.apis.CatchExceptionAssertJ.*;public class CatchExceptionsTest {@Testpublic void verifiesCauseType() {when(new ExceptionThrower()).someOtherMethod();then(caughtException()).isInstanceOf(RuntimeException.class).hasMessage("Runtime exception occurred").hasCauseExactlyInstanceOf(IllegalStateException.class).hasRootCauseExactlyInstanceOf(IllegalStateException.class);}
}

验证Hamcrest的自定义例外

为了验证我用我以前的Hamcrest匹配代码自定义异常后：

class CustomException extends RuntimeException {private final int code;public CustomException(int code) {this.code = code;}public int getCode() {return code;}
}class ExceptionCodeMatches extends TypeSafeMatcher<CustomException> {private int expectedCode;public ExceptionCodeMatches(int expectedCode) {this.expectedCode = expectedCode;}@Overrideprotected boolean matchesSafely(CustomException item) {return item.getCode() == expectedCode;}@Overridepublic void describeTo(Description description) {description.appendText("expects code ").appendValue(expectedCode);}@Overrideprotected void describeMismatchSafely(CustomException item, Description mismatchDescription) {mismatchDescription.appendText("was ").appendValue(item.getCode());}
}

和测试：

import org.junit.Test;import static com.googlecode.catchexception.CatchException.*;
import static org.junit.Assert.*;public class CatchExceptionsTest {@Testpublic void verifiesCustomException() {catchException(new ExceptionThrower(), CustomException.class).yetAnotherMethod(500);assertThat((CustomException) caughtException(), new ExceptionCodeMatcher(500));}
}