How unit test Eloquent model save failed ?

Hello,

I have difficulty testing the grounding of the save method.

CategoriesController@store

public function store(ArticleRequest $request)
    {
        $input = $request->input();
        $data = new Article($input);

        $response = DB::transaction(function () use ($data, $input) {
            try {
                $data->save();
            } catch (\Exception $e) {
                return response()->json($data->errors(), 422);
            }

            return response()->json($data, 201);
        });

        return $response;
    }

I would like to test the : `return response()->json($data->errors(), 422);``

Function test

public function testStore()
    {
        /**
         * |-------------------------------------------
         * | Success
         * |-------------------------------------------
         */
        $this->json('POST', '/api/articles', $this->input, $this->headers)
            ->assertStatus(201);

        /**
         * |-------------------------------------------
         * | Failed
         * |-------------------------------------------
         */
        $this->json('POST', '/api/articles', [], $this->headers)
            ->assertStatus(500);

    }

It works correctly, by in the coverage it indicates to me that the try catch is not tested.

How to make the save method fail to test try catch ?

I tried to mock the model

        $stub = $this->createMock(Illuminate\Database\Eloquent\Model::class);
        $stub->method('save')->willReturn(true);
        $this->assertFalse($stub->save($this->input));

But this does not apply to the save method of the model.

I also tested (in sandbox mode) :

        $this->mock = Mockery::mock(Illuminate\Database\Eloquent\Model::class);
        $this->app->instance(Illuminate\Database\Eloquent\Model::class, $this->mock);
        $this->mock
            ->shouldReceive('save')
            ->once()
            ->andReturn('foo');

        dump($this->call('GET', '/api/articles'));

Thanks for help.