In Mockito, `isNull()` and `notNull()` are two distinct matchers used for verifying the nullability of arguments in method calls. Here's a detailed explanation of each:
`isNull()`
- Purpose: The `isNull()` matcher is used to verify that an argument passed to a method is `null`. It checks whether the input is exactly `null`, meaning it does not match any other value.- Usage: This matcher is particularly useful when you need to ensure that a method is called with a `null` argument. For example, in a test scenario where you expect a method to handle `null` inputs, you can use `isNull()` to verify this behavior.
- Example:
java
verify(mockObject).method(isNull(String.class));
`notNull()`
- Purpose: The `notNull()` matcher is used to verify that an argument passed to a method is not `null`. It checks whether the input is any non-`null` value, regardless of its type or content.- Usage: This matcher is useful when you want to ensure that a method is called with a non-`null` argument. It does not care about the specific value as long as it is not `null`.
- Example:
java
verify(mockObject).method(notNull(String.class));
- Alias: `notNull()` has an alias named `isNotNull()`, which serves the same purpose but might be more readable in certain contexts.
Key Differences
- Nullability Check: The primary difference is that `isNull()` checks for `null` values, while `notNull()` checks for non-`null` values.- Usage Context: `isNull()` is used when you expect a method to be called with a `null` argument, whereas `notNull()` is used when you expect a non-`null` argument.
- Readability and Intent: Both matchers clearly convey their intent, but `notNull()` might be more commonly used to ensure that methods are called with valid, non-`null` arguments, which is often a requirement in robust programming.
In summary, `isNull()` and `notNull()` are complementary matchers in Mockito that help ensure the correct handling of `null` and non-`null` arguments in method calls, each serving a distinct purpose based on the expected behavior of the method under test.
Citations:[1] https://krossovochkin.com/posts/2021_09_11_mocking_matchers_api/
[2] https://www.lambdatest.com/automation-testing-advisor/selenium/methods/org.mockito.ArgumentMatchers.isNull
[3] https://www.reddit.com/r/SQL/comments/1q614u/difference_between_isnull_and_if_thing_is_null/
[4] https://stackoverflow.com/questions/3925191
[5] https://www.lambdatest.com/automation-testing-advisor/kotlin/methods/org.mockito.kotlin.Matchers.isNull
[6] https://gis.stackexchange.com/questions/203463/what-is-the-difference-between-null-and-is-not-null-in-qgis-filter-expression
[7] https://www.lambdatest.com/automation-testing-advisor/selenium/methods/org.mockito.ArgumentMatchers.notNull
[8] https://stevewall123.wordpress.com/2015/01/08/using-matches-for-null-parameter-with-mockito/
[9] https://stackoverflow.com/questions/4070207/what-is-the-difference-between-is-not-null-and-not-is-null
[10] https://www.reddit.com/r/SQL/comments/tekoum/what_are_pros_and_cons_of_using_nulls_vs_notnulls/
[11] https://stackoverflow.com/questions/3530124/differences-between-is-null-and-isnull-in-mysql/17555439