服务容器上下文绑定报错

哪位前辈帮忙答疑解惑一下
错误信息：
Target [App\Contracts\MyTest\IsTest] is not instantiable.

TestServiceProvider.php

public function register()
    {
        //
//        $this->app->singleton('TestT',Test::class);
        /*$this->app->singleton(
            \App\Contracts\MyTest\IsTest::class,
                \App\Units\Test\Contracts::class
        );*/
//        $this->app->bind(
//            \App\Contracts\MyTest\IsTest::class,
//            \App\Units\Test\Contracts::class
//        );
//        $this->app->bind(
//            \App\Contracts\MyTest\IsTest::class,
//            \App\Units\Test\Test::class
//        );
    // 上面的代码正常
        // 上下文绑定
        // IsTest 是一个接口，Contracts和Test是实现
        $this->app->when(HomeController::class)
            ->needs(IsTest::class)
            ->give(\App\Units\Test\Contracts::class);

        $this->app->when(TestController::class)
            ->needs(IsTest::class)
            ->give(\App\Units\Test\Test::class);
    }