如何使用JUnit来测试某些代码是否抛出异常?
我当然可以这样做:
@Test
public void testFooThrowsIndexOutOfBoundsException() {
boolean thrown = false;
try {
foo.doStuff();
} catch (IndexOutOfBoundsException e) {
thrown = true;
}
assertTrue(thrown);
}
我记得,对于这类情况,有一个注释或Assert.xyz之类的东西远没有JUnit那么笨拙,更符合JUnit的精神。
我在这里尝试了许多方法,但它们要么很复杂,要么不太符合我的要求。事实上,可以非常简单地编写一个助手方法:
public class ExceptionAssertions {
public static void assertException(BlastContainer blastContainer ) {
boolean caughtException = false;
try {
blastContainer.test();
} catch( Exception e ) {
caughtException = true;
}
if( !caughtException ) {
throw new AssertionFailedError("exception expected to be thrown, but was not");
}
}
public static interface BlastContainer {
public void test() throws Exception;
}
}
这样使用:
assertException(new BlastContainer() {
@Override
public void test() throws Exception {
doSomethingThatShouldExceptHere();
}
});
零依赖:无需mockito,无需powermock;在期末考试中表现很好。
我想评论一下这个问题的解决方案,它避免了任何与异常相关的JUnit代码。
我使用assertTrue(布尔值)和try/catch组合来查找要抛出的预期异常。下面是一个示例:
public void testConstructor() {
boolean expectedExceptionThrown;
try {
// Call constructor with bad arguments
double a = 1;
double b = 2;
double c = a + b; // In my example, this is an invalid option for c
new Triangle(a, b, c);
expectedExceptionThrown = false; // because it successfully constructed the object
}
catch(IllegalArgumentException e) {
expectedExceptionThrown = true; // because I'm in this catch block
}
catch(Exception e) {
expectedExceptionThrown = false; // because it threw an exception but not the one expected
}
assertTrue(expectedExceptionThrown);
}
我使用Java 8 lambdas的解决方案:
public static <T extends Throwable> T assertThrows(Class<T> expected, ThrowingRunnable action) throws Throwable {
try {
action.run();
Assert.fail("Did not throw expected " + expected.getSimpleName());
return null; // never actually
} catch (Throwable actual) {
if (!expected.isAssignableFrom(actual.getClass())) { // runtime '!(actual instanceof expected)'
System.err.println("Threw " + actual.getClass().getSimpleName()
+ ", which is not a subtype of expected "
+ expected.getSimpleName());
throw actual; // throw the unexpected Throwable for maximum transparency
} else {
return (T) actual; // return the expected Throwable for further examination
}
}
}
您必须定义FunctionalInterface,因为Runnable没有声明所需的抛出。
@FunctionalInterface
public interface ThrowingRunnable {
void run() throws Throwable;
}
方法如下:
class CustomException extends Exception {
public final String message;
public CustomException(final String message) { this.message = message;}
}
CustomException e = assertThrows(CustomException.class, () -> {
throw new CustomException("Lorem Ipsum");
});
assertEquals("Lorem Ipsum", e.message);