Find method dose not work in laravel controller

I have controller like this $test= test::find($id); return $test;

return null but when I change it to

 $test= test::where('id',$id)->get();
 return $test;

return all value of $test My migration is

 Schema::create('tests', function (Blueprint $table) {

        $table->increments('id');
        $table->string('user', 20);
 }),

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