When using Mockito argument matchers extensively, there are several performance considerations to keep in mind. While Mockito is generally efficient, the extensive use of argument matchers can introduce some overhead due to the way Mockito processes these matchers.
1. Matcher Processing Overhead**
- Argument Matcher Evaluation: When you use argument matchers like `eq()`, `any()`, or `anyString()`, Mockito needs to evaluate these matchers at runtime. This evaluation process can introduce a slight overhead compared to passing exact values directly. However, this overhead is typically negligible unless you are dealing with a very large number of invocations or complex matchers.2. Matcher Combination Rules**
- All Arguments Must Use Matchers: If you use an argument matcher for one argument, all arguments must use matchers. This rule can lead to more verbose code and potentially more overhead if you're using matchers for all arguments when only one needs a specific condition. For example, if a method has three parameters and you want to use `any()` for one of them, you must use matchers for the other two as well, even if you could have used exact values.3. Custom Matchers**
- Complex Logic: While Mockito provides a wide range of built-in matchers, you might need to create custom matchers for specific logic. Custom matchers can be more computationally expensive if they involve complex logic or operations. This is because they require implementing the `ArgumentMatcher` interface and defining a `matches()` method that can perform arbitrary checks.4. Verification Overhead**
- Verification with Matchers: When verifying interactions with mock objects using `verify()`, Mockito also uses matchers to check if the correct arguments were passed. Similar to stubbing, verification with matchers can introduce some overhead, especially if you're verifying multiple calls with complex matchers.5. Best Practices for Performance**
- Use Specificity Wisely: Use matchers with the right level of specificity. For example, `anyInt()` is less specific and faster than `eq(4)`, but using `eq(4)` when you need to verify a specific value is more precise and doesn't significantly impact performance.- Avoid Unnecessary Complexity: Avoid using custom matchers unless necessary. If a test requires complex logic to match arguments, consider simplifying the test or using existing matchers creatively.
- Profile Your Tests: If you notice performance issues in your tests, profile them to identify bottlenecks. It's rare for Mockito matchers to be the primary cause of significant performance issues, but it's always good to verify.
In summary, while Mockito argument matchers do introduce some overhead, this is generally not a significant concern unless you are dealing with extremely complex or performance-critical tests. The benefits of using matchersâsuch as flexibility and clarity in test codeâusually outweigh the minor performance costs.
Citations:[1] https://stackoverflow.com/questions/56559146/junit-using-eq-argument-matcher-vs-passing-string-directly/56572275
[2] https://www.digitalocean.com/community/tutorials/mockito-argument-matchers-any-eq
[3] https://kenkousen.substack.com/p/tales-from-the-jar-side-a-mockito
[4] https://www.softwaretestinghelp.com/mockito-matchers/
[5] https://www.toptal.com/java/a-guide-to-everyday-mockito
[6] https://github.com/etorreborre/specs2/issues/854
[7] https://www.lambdatest.com/automation-testing-advisor/selenium/classes/org.mockito.AdditionalMatchers
[8] https://stackoverflow.com/questions/73046134/when-should-i-use-argument-matcher-or-passing-argument-directly-when-mockito-uni