@@ -12,6 +12,8 @@ import (

 	"github.com/docker/docker/api/types/container"

 	"github.com/docker/docker/errdefs"

+	"gotest.tools/v3/assert"

+	is "gotest.tools/v3/assert/cmp"

 )

 func TestContainerDiffError(t *testing.T) {

@@ -19,28 +21,33 @@ func TestContainerDiffError(t *testing.T) {

 		client: newMockClient(errorMock(http.StatusInternalServerError, "Server error")),

 	}

 	_, err := client.ContainerDiff(context.Background(), "nothing")

-	if !errdefs.IsSystem(err) {

-		t.Fatalf("expected a Server Error, got %[1]T: %[1]v", err)

-	}

+	assert.Check(t, is.ErrorType(err, errdefs.IsSystem))

 }

 func TestContainerDiff(t *testing.T) {

-	expectedURL := "/containers/container_id/changes"

+	const expectedURL = "/containers/container_id/changes"

+

+	expected := []container.FilesystemChange{

+		{

+			Kind: container.ChangeModify,

+			Path: "/path/1",

+		},

+		{

+			Kind: container.ChangeAdd,

+			Path: "/path/2",

+		},

+		{

+			Kind: container.ChangeDelete,

+			Path: "/path/3",

+		},

+	}

+

 	client := &Client{

 		client: newMockClient(func(req *http.Request) (*http.Response, error) {

 			if !strings.HasPrefix(req.URL.Path, expectedURL) {

-				return nil, fmt.Errorf("Expected URL '%s', got '%s'", expectedURL, req.URL)

+				return nil, fmt.Errorf("expected URL '%s', got '%s'", expectedURL, req.URL)

 			}

-			b, err := json.Marshal([]container.FilesystemChange{

-				{

-					Kind: container.ChangeModify,

-					Path: "/path/1",

-				},

-				{

-					Kind: container.ChangeAdd,

-					Path: "/path/2",

-				},

-			})

+			b, err := json.Marshal(expected)

 			if err != nil {

 				return nil, err

 			}

@@ -52,10 +59,6 @@ func TestContainerDiff(t *testing.T) {

 	}

 	changes, err := client.ContainerDiff(context.Background(), "container_id")

-	if err != nil {

-		t.Fatal(err)

-	}

-	if len(changes) != 2 {

-		t.Fatalf("expected an array of 2 changes, got %v", changes)

-	}

+	assert.Check(t, err)

+	assert.Check(t, is.DeepEqual(changes, expected))

 }