verify

Learn call verification with verify.

verify

With verify(mock) you check the calls made on a mock. You can test whether a specific method was called with a specific input, and how many times.

service.register("Alex");

verify(repo).save(any(User.class));
verify(mail, times(1)).send("Alex");

This is how you verify the side effects of the code under test. The interaction is checked, not the return value. Qualifiers like times, never, atLeast specify the frequency.

Call count qualifiers

With verify you can also check the call count. times(n) means exactly n times, never() means never, atLeast(n) means at least n times.

verify(mail, times(2)).send("Alex");
verify(repo, never()).delete(anyInt());
verify(logger, atLeast(1)).info(anyString());

This verifies that side effects happen with exactly the expected frequency. Errors such as duplicate emails or accidental deletes are caught. Tests become more precise.

Exercise Count interactions with a Logger

Define a Logger interface (void info(String msg)). A Counter class tracks the number of info calls. In Counter the log(String msg) method increments the counter each call. In a VerifyDemo class write main; call log three times and print the counter.

Show example solution

interface Logger {
    void info(String msg);
}

class Counter implements Logger {
    int count = 0;
    public void info(String msg) {
        count++;
    }
}

class VerifyDemo {
    public static void main(String[] args) {
        Counter c = new Counter();
        c.info("a");
        c.info("b");
        c.info("c");
        System.out.println(c.count);
    }
}

Test yourself

What does verify check?
- The mock's return value
- The test duration
- The mock's type
- The calls made on the mock
Show answer

The calls made on the mock — verify checks the calls made on the mock.
Match the qualifiers

times(2)

Exactly two times
never()

Never called
atLeast(1)

At least once
atMost(3)

At most three times

Complete the verify call

service.register("Ayşe");

____(mail).send("Ayşe");

Show answer

service.register("Ayşe");

verify(mail).send("Ayşe");

Next lesson: ArgumentMatchers

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