public function testUserCanExtendWithCustomFunctions() { Arrays::extend('fooify', function ($array) { return 'bar'; }); $this->assertEquals('bar', Arrays::fooify(['foo'])); Strings::extend('unfooer', function ($string) { return Strings::replace($string, 'foo', 'bar'); }); $this->assertEquals('bar', Strings::unfooer('foo')); }