What are some common use cases for argument matchers in Mockito

Stubbing Generic Behaviors

When you're testing a method that doesn't depend on specific input values, you can use argument matchers like `any()`, `anyString()`, `anyInt()`, etc., to stub its behavior. For example, if you have a method `bool(String str, int i, Object obj)`, you can stub it to return `true` for any input:

java
Foo mockFoo = mock(Foo.class);
when(mockFoo.bool(anyString(), anyInt(), any(Object.class))).thenReturn(true);

This way, no matter what string, integer, or object you pass to `bool()`, it will return `true`.

Matching Specific Values

If you need to match a specific value for one argument while keeping others generic, you can use `eq()` along with other matchers. For instance:

java
when(mockFoo.bool(eq("false"), anyInt(), any(Object.class))).thenReturn(false);

Here, the method will return `false` only if the string argument is `"false"`, regardless of the integer and object values.

Verification

Argument matchers are also useful for verifying that a method was called with certain arguments. You can use `verify()` with matchers to check if a method was invoked with specific or generic conditions:

java
verify(mockFoo).bool(anyString(), anyInt(), any(Object.class));

This verifies that `bool()` was called at least once with any string, integer, and object.

Complex Conditions

Mockito provides additional matchers for more complex conditions, such as `gt()`, `lt()`, `geq()`, `leq()`, which can be used for numeric comparisons. You can also combine matchers using logical operations like `or()`, `and()`, and `not()`:

java
when(mockFoo.bar(any(byte[].class), aryEq(new String[] { "A", "B" }), gt(10))).thenReturn(11);

This stubs the `bar()` method to return `11` if it's called with any byte array, the string array `["A", "B"]`, and an integer greater than `10`.

Custom Matchers

If the built-in matchers aren't sufficient, you can create custom matchers using `argThat()`. This allows you to define a custom condition for matching arguments:

java
ArgumentMatcher hasLuck = file -> file.getName().endsWith("luck");
when(fileFilter.accept(argThat(hasLuck))).thenReturn(true);

This stubs `accept()` to return `true` if the file name ends with `"luck"`.

In summary, argument matchers are versatile tools in Mockito that help you write more flexible and robust tests by allowing generic or specific matching of method arguments during stubbing and verification.