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。
使用可以与JUnit一起使用的AssertJ断言:
import static org.assertj.core.api.Assertions.*;
@Test
public void testFooThrowsIndexOutOfBoundsException() {
Foo foo = new Foo();
assertThatThrownBy(() -> foo.doStuff())
.isInstanceOf(IndexOutOfBoundsException.class);
}
它比@Test(expected=IndexOutOfBoundsException.class)更好,因为它保证了测试中的预期行抛出了异常,并允许您更容易地检查有关异常的详细信息,例如消息:
assertThatThrownBy(() ->
{
throw new Exception("boom!");
})
.isInstanceOf(Exception.class)
.hasMessageContaining("boom");
Maven/Gradle说明。
在JUnit 4或更高版本中,您可以如下测试异常
@Rule
public ExpectedException exceptions = ExpectedException.none();
这提供了许多可以用来改进JUnit测试的特性。如果您看到下面的示例,我将测试异常的3个方面。
引发的异常类型异常消息异常的原因
public class MyTest {
@Rule
public ExpectedException exceptions = ExpectedException.none();
ClassUnderTest classUnderTest;
@Before
public void setUp() throws Exception {
classUnderTest = new ClassUnderTest();
}
@Test
public void testAppleisSweetAndRed() throws Exception {
exceptions.expect(Exception.class);
exceptions.expectMessage("this is the exception message");
exceptions.expectCause(Matchers.<Throwable>equalTo(exceptionCause));
classUnderTest.methodUnderTest("param1", "param2");
}
}
JUnit框架具有assertThrows()方法:
ArithmeticException exception = assertThrows(ArithmeticException.class, () ->
calculator.divide(1, 0));
assertEquals("/ by zero", exception.getMessage());
对于JUnit 5,它位于org.unit.jupiter.api.Assertions类中;对于JUnit 4.13,它位于org.JUnit.Assert类中;对于JUnit4的早期版本:只需将org.JUnit.jupiter:junitjupiterapi上的引用添加到项目中,就可以从JUnit5获得非常好的工作版本。
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);