Issue
I'm trying to test that a cache I created is working properly, and duplicate calls to a method aren't actually called multiple times, but loaded from my cache.
I'm using LoadingCache from Google Guava to accomplish this.
So my naive approach was to create a spy, and verify that the method was called once. I then figured out that because spy() is a decorator, I can only see if the method was called on that object. Since the method is being called by LoadingCache, my spy cannot verify it.
How do I best test that my cache is being used properly?
(note: I could make a LoadingCache dependency, and check that the correct method is called, but then I don't know if my cache is working. Maybe the hash is calculated in a way I didn't anticipate, and so it actually is calling the method every time. I want to actually see the effect)
private final LoadingCache<TaskDetails, byte[]> cache;
...
cache = CacheBuilder.newBuilder()
.maximumSize(cacheSize)
.expireAfterAccess(Duration.ofMinutes(cacheDurationInMinutes))
.build(CacheLoader.from(this::doTask));
public byte[] taskCaller(...) {
...
return cache.getUnchecked();
}
public byte[] doTask(...) {
if(something.doSomething() ... ) {
...
}
First test attempt doesn't work, Mockito says: Wanted but not invoked (the method was "never called", since the spy doesn't know the cache called it)
@Test
public void test() {
// given
TaskService spy = spy(
new TaskService(...)
);
// when
for (int i = 0; i < 3; i++) {
spy.taskCaller(...);
}
// then
//if caching is working, we should only do the real work once
verify(spy, times(1)).doTask(any(TaskDetails.class));
}
Second attempt: NullPointerException on first statement in the method ( something.doSomething() ), I'm not completely sure why, but I'm convinced for the same reason as before
@Test
public void test() {
// given
TaskService spy = spy(
new TaskService(...)
);
final int[] counter = {0};
when(spy.doTask(any())).thenAnswer(invocation -> {
counter[0]++;
return new byte[]{0,0,0,0};
});
// when
int run = 3;
for (int i = 0; i < run; i++) {
spy.taskCaller(...);
}
// then
//if caching is working, we should only do the real work once
assertThat(run).isEqualTo(counter[0]);
verify(spy, times(1)).doTask(any(TaskDetails.class));
}
Solution
Two ideas:
- Enable cache stats recording, interact with the cache, get the cache stats, then verify that the load count (and possibly other stats) are what you expect.
- Make your
CacheLoader
a separate named class rather than a method reference, an instance of which is passed toCacheBuilder.build()
, and arrange for that instance to be a mock in your test. You can then verify method call counts and arguments on your mock loader.
Answered By - isomeme