Optional $skipWhenEmpty parameter for #[DataProvider] and #[DataProviderExternal]

[sebastianbergmann]

This implements an optional $skipWhenEmpty parameter (defaulting to false) for the #[DataProvider] and #[DataProviderExternal] attributes. When set to true, a data provider that returns an empty iterable will cause the test to be skipped instead of triggering an error.

Usage:

#[DataProvider('provider', skipWhenEmpty: true)]
public function testSomething(string $value): void
{
    // ...
}

Note: Parameter names are not covered by the backward compatibility promise for PHPUnit.

When all data providers for a test method return no data and at least one of them has skipWhenEmpty: true, the test is created as a single test case that skips itself with the message "The data provider for this test provided no data, which is explicitly permitted". The default behavior (error on empty data provider) is unchanged.

Closes #6404.

[sebastianbergmann]

@stof Is this what you had in mind?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.91%. Comparing base (043a636) to head (5fe6f25).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #6565   +/-   ##
=========================================
  Coverage     96.90%   96.91%           
- Complexity     7604     7613    +9     
=========================================
  Files           819      819           
  Lines         23512    23533   +21     
=========================================
+ Hits          22785    22806   +21     
  Misses          727      727           

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