Adds new when() method

[mertasan]

Q	A
Bug fix?	no
New feature?	yes

It makes some expectations work conditionally.

when() is preferably used as an alternative to the skip() method, no need to write extra tests.

Examples

Before:

it('mysql test', function () {

   expect(new Foo())
         ->mysql
         ->toBeTrue();

})->skip(fn() => DB::getDriverName() === 'mysql', 'Only runs when using mysql');

it('sqlite test', function () {

   expect(new Foo())
         ->sqlite
         ->toBeTrue();

})->skip(fn() => DB::getDriverName() === 'sqlite', 'Only runs when using sqlite');

After:

it('database test', function () {

    $driver = DB::getDriverName();
    
    expect(new Foo())
        ->when($driver === 'mysql',
            fn($foo) => $foo->mysql->toBeTrue()
        )
        ->when($driver === 'sqlite',
            fn($foo) => $foo->sqlite->toBeTrue()
        )
        ->bar->toEqual('bar');

});

For more examples, please review the tests.

Thank you.

[nunomaduro]

Can you pull request the docs please?

[nunomaduro]

Can you also document the unless? b43a598

[mertasan]

I'll make PR, thank you.