go-table-testing-arg-functions

Example on how to use fields/args generators in table-tests.

Generic Pattern to build table-driven tests with args/field "factories":

1. 💡 Generate test stub

Generate table-driven test stub first, like this:

// Typical autogenerated code for table-tests, nothing special here:
func TestProductsForUser_Get(t *testing.T) {
    type fields struct {
        userSvc    UserService
        productSvc ProductService
    }
    type args struct {
        userID model.UserID
    }
    tests := []struct {
        name    string
        fields  fields
        args    args
        want    []model.Product
        wantErr bool
    }{
        // TODO: Add test cases.
    }
    for _, tt := range tests {
        tt := tt
        t.Run(tt.name, func(t *testing.T) {
            pu := &ProductsForUser{
                userSvc:    tt.fields.userSvc,
                productSvc: tt.fields.productSvc,
            }
            got, err := pu.Get(tt.args.userID)
            if (err != nil) != tt.wantErr {
                t.Errorf("Get() error = %v, wantErr %v", err, tt.wantErr)
                return
            }
            if !reflect.DeepEqual(got, tt.want) {
                t.Errorf("Get() got = %v, want %v", got, tt.want)
            }
        })
    }
}

NOTE: And do not forget about assignments tt := tt in case those will be converted to parallel tests in the future (using t.Parallel()):

    for _, tt := range tests {
        tt := tt // <-- THIS IS IMPORTANT
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel()
            // write actual test			
        })
    }

---

2. ⚙️ Refactor code

Change the args and/or fields parameter to be a function that returns filled args/fields respectively:

    type fields struct {
        userSvc    UserService
        productSvc ProductService
    }
    type args struct {
        userID model.UserID
    }
    tests := []struct {
        name       string
        fieldsFunc func(t *testing.T, ctrl *gomock.Controller) fields // <-- THIS IS a "factory"
        args       args // <-- In some cases, this also can be converted to a "factory" 
        want       []model.Product
        wantErr    bool
    }{
        // TODO: Add test cases.
    }

Typical "factory" function signature may look like:

func(t *testing.T) fields

or in case of GoMock

func(t *testing.T, ctrl *gomock.Controller) fields

---

3. 🎯 Benefits

The benefits of using this "factory" approach to prepare all the fields inside args/fields are:

• the ability to code custom preparation logic;
• the ability to build one mock/stub that is dependent on another one, i.e., introduce coupling between components;

As shown in the example:

fieldsFunc: func(t *testing.T, ctrl *gomock.Controller) fields {
    t.Helper()

    userSvc := mock_usecases.NewMockUserService(ctrl)
    userSvc.EXPECT().Get(gomock.Any()).Return(model.User{
        ID:   "some-user-ID",
        Name: "name",
    }, nil).Times(1)
    productSvc := mock_usecases.NewMockProductService(ctrl)
    productSvc.EXPECT().GetProducts(gomock.Any()).Return(nil, errors.New("get products")).Times(1)
    return fields{
        userSvc:    userSvc,
        productSvc: productSvc,
    }
}

NOTE: Do not forget to use t.Helper() function in the beginning of the "factory".

---

4. 🕶️ Useful IntelliJ Live Templates

📖 mtest

Description: Mocked table-driven Test with gomock

Note: assumed testing library: GoMock

func Test$NAME$(t *testing.T) {
	type fields struct {
	}
	type args struct {
	}
	tests := []struct {
		name          string
		fieldsFactory func(t *testing.T, ctrl *gomock.Controller) fields
		argsFactory   func(t *testing.T, ctrl *gomock.Controller) args
		args          args
	}{
        {
			name: "good",
			fieldsFactory: func(t *testing.T, ctrl *gomock.Controller) fields {
				t.Helper()
				
				return fields{}
			},
			argsFactory: func(t *testing.T, ctrl *gomock.Controller) args {
				t.Helper()
				
				return args{}
			},
			args: args{},
		},
	}
	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			ctrl := gomock.NewController(t)

			fields := tt.fieldsFactory(t, ctrl)
			args := tt.argsFactory(t, ctrl)

			fields = fields
			args = args$END$
		})
	}
}

📖 stest

Description: Test with subtests

Note: assumed testing library: Testify

func Test$NAME$(t *testing.T) {
    t.Run("good", func(t *testing.T) {
        r := require.New(t)

        r = r$END$
    })
}

📖 erris

Description: If error IS()

if errors.Is($ERR$, $TARTGET_ERR$) {
    $END$
}

📖 erras

Description: If error AS()

var $TARTGET_ERR$ *$TARGET_ERR_TYPE$
if errors.Is($ERR$, &$TARTGET_ERR$) {
    $END$
}

📖 set

Description: Set type

map[$KEY_TYPE$]struct{}