如何在可完成的将来测试异常? [英] How can I test exception in completable future?

问题描述

我一直在将某些代码转换为异步代码.原始的单元测试使用了注释@Test(expected = MyExcpetion.class)，但是我认为这不会起作用，因为我要声明的异常包装在java.util.concurrent.ExcutionException中.我确实尝试过这样称呼我的未来，但是我的断言仍然失败，我不喜欢必须在return null

I have been converting some code to be asynchronous. The original unit test used the annotation @Test(expected = MyExcpetion.class) but I don't think this will work because the exception I want to assert on is wrapped in java.util.concurrent.ExcutionException . I did try calling my future like this but my assertion is still failing and I don't love that I had to add in return null

myApiCall.get(123).exceptionally((ex) -> {
 assertEquals(ex.getCause(),MyCustomException.class)
 return null
}

我也尝试过这种口味，但仍然无法使用

I also tried this flavor but still not working

myApiCall.get(123).exceptionally((ex) -> {
 assertThat(ex.getCause())
  .isInstanceOF(MyException.class)
  .hasMessage("expected message etc")
 return null;
}

如果找不到ID，我的API只会引发异常.我应该如何正确测试呢?无论如何，我可以使用该原始注释吗?

My API just throws exception if it can't find id. How should I be properly testing this? Can I use that original annotation in anyway?

运行时，我的api调用到达db.在此测试中，我将未来设置为返回错误，因此它实际上不会尝试与任何事物进行通信.被测试的代码看起来像这样

my api call reaches out to db when run. In this test I am setting up my future to return an error so it doesn't actually try to communicate with anything. the code under test looks like this

 public class myApiCall  { 
   public completableFuture get(final String id){
   return myService.getFromDB(id)
    .thenApply( 
       //code here looks at result and if happy path then returns it after 
       //doing some transformation 
      //otherwise it throws exception 
   )
  }
 }

在单元测试中，我强制myService.getFromDB(id)返回错误数据，以便我可以测试异常，还可以保持此单元测试不会与db等保持联系.

in the unit test I force myService.getFromDB(id) to return bad data so I can test exception and also keep this a unit test don't reach out to db etc.

推荐答案

假设使用0调用您的API会抛出异常:

Let's assume your API throws if called with 0:

public static CompletableFuture<Integer> apiCall(int id) {
  return CompletableFuture.supplyAsync(() -> {
    if (id == 0) throw new RuntimeException("Please not 0!!");
    else return id;
  });
}

您可以使用以下代码测试它是否按预期工作(我正在使用TestNG，但我怀疑将其转换为JUnit测试不会太困难):

You can test that it works as expected with the following code (I'm using TestNG but I suspect it won't be too difficult to translate into a JUnit test):

@Test public void test_ok() throws Exception {
  CompletableFuture<Integer> result = apiCall(1);
  assertEquals(result.get(), (Integer) 1);
}

@Test(expectedExceptions = ExecutionException.class,
      expectedExceptionsMessageRegExp = ".*RuntimeException.*Please not 0!!")
public void test_ex() throws Throwable {
  CompletableFuture<Integer> result = apiCall(0);
  result.get();
}

请注意，第二个测试使用了这样的事实，即ExecutionException消息将包含原始异常类型和消息，并使用正则表达式捕获期望.如果使用JUnit无法做到这一点，则可以在try/catch块中调用result.get()，在catch块中调用throw e.getCause();.换句话说，是这样的:

Note that the second test uses the fact that the ExecutionException message will contain the original exception type and message and captures the expectation with a regex. If you can't do that with JUnit, you can call result.get() in a try/catch block and call throw e.getCause(); in the catch block. In other words, something like this:

@Test(expectedExceptions = RuntimeException.class,
      expectedExceptionsMessageRegExp = "Please not 0!!")
public void test_ex() throws Throwable {
  CompletableFuture<Integer> result = apiCall(0);
  try {
    result.get();
  } catch (ExecutionException e) {
    throw e.getCause();
  }
}

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