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);
}
使用Java 8,您可以创建一个方法,将要检查的代码和预期异常作为参数:
private void expectException(Runnable r, Class<?> clazz) {
try {
r.run();
fail("Expected: " + clazz.getSimpleName() + " but not thrown");
} catch (Exception e) {
if (!clazz.isInstance(e)) fail("Expected: " + clazz.getSimpleName() + " but " + e.getClass().getSimpleName() + " found", e);
}
}
然后在测试中:
expectException(() -> list.sublist(0, 2).get(2), IndexOutOfBoundsException.class);
优点:
不依赖任何库本地化检查-更精确,如果需要,允许在一个测试中有多个这样的断言易于使用