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。
例如,您想为下面提到的代码片段编写Junit
public int divideByZeroDemo(int a,int b){
return a/b;
}
public void exceptionWithMessage(String [] arr){
throw new ArrayIndexOutOfBoundsException("Array is out of bound");
}
上面的代码用于测试可能发生的某些未知异常,下面的代码用于使用自定义消息断言某些异常。
@Rule
public ExpectedException exception=ExpectedException.none();
private Demo demo;
@Before
public void setup(){
demo=new Demo();
}
@Test(expected=ArithmeticException.class)
public void testIfItThrowsAnyException() {
demo.divideByZeroDemo(5, 0);
}
@Test
public void testExceptionWithMessage(){
exception.expectMessage("Array is out of bound");
exception.expect(ArrayIndexOutOfBoundsException.class);
demo.exceptionWithMessage(new String[]{"This","is","a","demo"});
}
例如,您想为下面提到的代码片段编写Junit
public int divideByZeroDemo(int a,int b){
return a/b;
}
public void exceptionWithMessage(String [] arr){
throw new ArrayIndexOutOfBoundsException("Array is out of bound");
}
上面的代码用于测试可能发生的某些未知异常,下面的代码用于使用自定义消息断言某些异常。
@Rule
public ExpectedException exception=ExpectedException.none();
private Demo demo;
@Before
public void setup(){
demo=new Demo();
}
@Test(expected=ArithmeticException.class)
public void testIfItThrowsAnyException() {
demo.divideByZeroDemo(5, 0);
}
@Test
public void testExceptionWithMessage(){
exception.expectMessage("Array is out of bound");
exception.expect(ArrayIndexOutOfBoundsException.class);
demo.exceptionWithMessage(new String[]{"This","is","a","demo"});
}
Java 8解决方案
如果您想要一个解决方案:
利用Java 8 lambda不依赖任何JUnit魔法允许您检查单个测试方法中的多个异常检查测试方法中特定的一组行(而不是整个测试方法中的任何未知行)是否引发异常生成引发的实际异常对象,以便您可以进一步检查它
下面是我编写的实用函数:
public final <T extends Throwable> T expectException( Class<T> exceptionClass, Runnable runnable )
{
try
{
runnable.run();
}
catch( Throwable throwable )
{
if( throwable instanceof AssertionError && throwable.getCause() != null )
throwable = throwable.getCause(); //allows testing for "assert x != null : new IllegalArgumentException();"
assert exceptionClass.isInstance( throwable ) : throwable; //exception of the wrong kind was thrown.
assert throwable.getClass() == exceptionClass : throwable; //exception thrown was a subclass, but not the exact class, expected.
@SuppressWarnings( "unchecked" )
T result = (T)throwable;
return result;
}
assert false; //expected exception was not thrown.
return null; //to keep the compiler happy.
}
(摘自我的博客)
使用方法如下:
@Test
public void testMyFunction()
{
RuntimeException e = expectException( RuntimeException.class, () ->
{
myFunction();
} );
assert e.getMessage().equals( "I haz fail!" );
}
public void myFunction()
{
throw new RuntimeException( "I haz fail!" );
}