Verification times (times, never, atLeast) in JUnit

Introduction

We use verification times to check how many times a method was called in a test. This helps us make sure our code behaves as expected.

When you want to confirm a method was called exactly a certain number of times.

When you want to check that a method was never called during a test.

When you want to verify a method was called at least a minimum number of times.

Syntax

JUnit

verify(mockObject, times(n)).methodCall();
verify(mockObject, never()).methodCall();
verify(mockObject, atLeast(n)).methodCall();

verify checks the method call on the mock object.

times(n) means exactly n times, never() means zero times, and atLeast(n) means n or more times.

Examples

Check that add("item") was called exactly twice on mockList.

JUnit

verify(mockList, times(2)).add("item");

Check that clear() was never called on mockList.

JUnit

verify(mockList, never()).clear();

Check that add("item") was called at least once on mockList.

JUnit

verify(mockList, atLeast(1)).add("item");

Sample Program

This test creates a mock list and calls add("apple") twice. It then verifies the method calls using times(2), never(), and atLeast(1). If all verifications pass, it prints a success message.

JUnit

import static org.mockito.Mockito.*;
import java.util.List;

public class VerificationTimesTest {
    public static void main(String[] args) {
        List<String> mockList = mock(List.class);

        mockList.add("apple");
        mockList.add("apple");

        // Verify add("apple") called exactly 2 times
        verify(mockList, times(2)).add("apple");

        // Verify clear() was never called
        verify(mockList, never()).clear();

        // Verify add("apple") called at least once
        verify(mockList, atLeast(1)).add("apple");

        System.out.println("All verifications passed.");
    }
}

Important Notes

If a verification fails, Mockito throws an exception and the test fails.

Use never() to ensure no unwanted calls happen.

atLeast(n) is useful when you expect multiple calls but exact count is not fixed.

Summary

Verification times help check how often methods are called in tests.

times(n) means exactly n calls, never() means zero calls, and atLeast(n) means n or more calls.

These checks make tests more precise and reliable.

Practice

1. Which Mockito verification method checks that a method was called exactly 3 times?

easy

A. verify(mock, atMost(3)).method()

B. verify(mock, never()).method()

C. verify(mock, atLeast(3)).method()

D. verify(mock, times(3)).method()

Solution

1. Step 1: Understand times(n) usage

   The times(n) method verifies that the method was called exactly n times.

2. Step 2: Match the exact call count

   Since the question asks for exactly 3 calls, times(3) is the correct choice.

3. Final Answer:

   verify(mock, times(3)).method() -> Option D

4. Quick Check:

   Exact call count = times(n) [OK]

Hint: Use times(n) for exact call count verification [OK]

Common Mistakes:

• Confusing times(n) with atLeast(n)
• Using never() when calls exist
• Using atMost(n) instead of times(n)

2. Which of the following is the correct syntax to verify that a method was never called using Mockito?

easy

A. verify(mock, never()).method();

B. verify(mock, atLeast(0)).method();

C. verify(mock, times(0));

D. verify(mock).never().method();

Solution

1. Step 1: Identify the correct method for zero calls

   Mockito provides never() to verify that a method was not called at all.

2. Step 2: Check syntax correctness

   The correct syntax is verify(mock, never()).method();. Using times(0) also works but never() is clearer and preferred.

3. Final Answer:

   verify(mock, never()).method(); -> Option A

4. Quick Check:

   No calls = never() [OK]

Hint: Use never() to verify zero calls clearly [OK]

Common Mistakes:

• Using times(0) instead of never() for clarity
• Incorrect chaining like verify(mock).never()
• Using atLeast(0) which always passes

3. Given the following code snippet:

verify(mock, atLeast(2)).process();

Which statement is true about the verification?

medium

A. The method process() must be called exactly 2 times.

B. The method process() must be called at most 2 times.

C. The method process() must be called at least 2 times or more.

D. The method process() must never be called.

Solution

1. Step 1: Understand atLeast(n) meaning

   The atLeast(n) method verifies that the method was called at least n times, meaning 2 or more times.

2. Step 2: Match the verification condition

   Since the code uses atLeast(2), it means the method must be called 2 or more times, not exactly 2.

3. Final Answer:

   The method process() must be called at least 2 times or more. -> Option C

4. Quick Check:

   Minimum calls = atLeast(n) [OK]

Hint: atLeast(n) means minimum n calls, not exact [OK]

Common Mistakes:

• Confusing atLeast(n) with times(n)
• Thinking atLeast(n) means at most n
• Assuming never() means zero calls only

4. Identify the error in this Mockito verification:

verify(mock, never).execute();

medium

A. Using times() instead of never()

B. Missing parentheses after never()

C. Incorrect method name execute()

D. No error, syntax is correct

Solution

1. Step 1: Check syntax of never()

   The never() method requires parentheses to be called as a method.

2. Step 2: Identify missing parentheses

   The code uses never without parentheses, which is a syntax error.

3. Final Answer:

   Missing parentheses after never() -> Option B

4. Quick Check:

   never() requires parentheses [OK]

Hint: Always add () after never to avoid syntax errors [OK]

Common Mistakes:

• Omitting parentheses after never
• Confusing never with times(0)
• Assuming method name causes error

5. You want to verify that a method update() was called at least once but no more than 5 times. Which Mockito verification code correctly expresses this?

hard

A. verify(mock, atLeast(1)).update(); verify(mock, atMost(5)).update();

B. verify(mock, times(1)).update(); verify(mock, times(5)).update();

C. verify(mock, never()).update();

D. verify(mock, atLeast(5)).update();

Solution

1. Step 1: Understand the requirement

   The method update() must be called at least once and at most 5 times.

2. Step 2: Use correct verification methods

   Use atLeast(1) to check minimum calls and atMost(5) to check maximum calls.

3. Step 3: Combine verifications

   Both verifications must be done separately to ensure the call count is between 1 and 5.

4. Final Answer:

   verify(mock, atLeast(1)).update(); verify(mock, atMost(5)).update(); -> Option A

5. Quick Check:

   Range check = atLeast + atMost [OK]

Hint: Combine atLeast(n) and atMost(m) for call count range [OK]

Common Mistakes:

• Using times() twice with different values
• Using never() when calls exist
• Using only atLeast(5) which ignores max limit