golden.go

// Copyright 2023 Cisco Systems, Inc. and its affiliates
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// SPDX-License-Identifier: Apache-2.0

// Package golden will contain some utility functions for golden file testing
//
// Golden File Testing pattern explained here:
// 		https://ieftimov.com/posts/testing-in-go-golden-files/
//
// # PopulateGoldenFiles will need to be added to the first test run and then removed
//
// Golden Files are populated and asserted based on the current runs test name
// t should be of a type *testing.T ref:[https://pkg.go.dev/testing#T]
// TODO this package has many limitations, e.g. only works with JSON and Structs, and it's not currently used by anyone.
//      Consider to remove it or improve it
package golden

import (
	"encoding/json"
	"github.com/google/go-cmp/cmp"
	"github.com/iancoleman/strcase"
	"github.com/sergi/go-diff/diffmatchpatch"
	"os"
	"path/filepath"
	"reflect"
	"strings"
)

const (
	MarshalPrefix = ""
	MarshalIndent = "    "
)

type GoldenFileTestingT interface {
	Fatalf(format string, args ...any)
	Errorf(format string, args ...any)
	Name() string
}

// PopulateGoldenFiles will write golden files to the according path returned from
// the GetGoldenFilePath function. The function will marshal the data into JSON.
// data should be of a type struct and not []byte or string.
// TODO review this function: if the function fails the test at beginning, what's the point to have it?
func PopulateGoldenFiles(t GoldenFileTestingT, data interface{}) {
	t.Errorf("Running PopulateGoldenFiles will result in a failed test.")
	if reflect.ValueOf(data).Kind() != reflect.Struct {
		t.Fatalf("expected data to be of type struct and not of type: %v", reflect.ValueOf(data).Kind())
	}
	goldenFilePath := GetGoldenFilePath(t)
	b, err := json.MarshalIndent(data, MarshalPrefix, MarshalIndent)
	if err != nil {
		t.Fatalf("unable to marshal to json: %v", err)
	}

	if _, err := os.Stat(goldenFilePath); err == nil {
		t.Fatalf("cannot use this function to update golden files")
	}

	err = os.MkdirAll(filepath.Dir(goldenFilePath), 0755)
	if err != nil {
		t.Fatalf("unable to mkdir to golden file path")
	}
	err = os.WriteFile(goldenFilePath, b, 0600)
	if err != nil {
		t.Fatalf("unable to write golden file: %v", err)
	}
}

// GetGoldenFilePath will typically return the path in the form ./testdata/golden/<sub-test-name>/<table_driven_test_name>.json
// However, if the test is not run in a subtest or table driven test, the path may differ. However, the last portion
// of the path will always become the golden json name.
func GetGoldenFilePath(t GoldenFileTestingT) string {
	fullName := t.Name()
	splitName := strings.Split(fullName, "/")
	// we expect 3 parts. TestName, SubTest, TableDrivenTest
	goldenFilePath := filepath.Join("testdata", "golden")
	for i, part := range splitName {
		if i == len(splitName)-1 {
			// if this is the last part, use it as the .json
			part = strcase.ToSnake(part)
			goldenFilePath = filepath.Join(goldenFilePath, part+".json")
			break
		}
		goldenFilePath = filepath.Join(goldenFilePath, part)
	}
	return goldenFilePath
}

// Assert will assert that the data matches what is in the golden file.
// data should be of a type struct and not []byte or string. The function will
// marshal the data into JSON.
// The diff will be represented in a colored diff
func Assert(t GoldenFileTestingT, data interface{}) {
	if reflect.ValueOf(data).Kind() != reflect.Struct {
		t.Fatalf("expected data to be of type struct")
	}
	goldenData, err := os.ReadFile(GetGoldenFilePath(t))
	if err != nil {
		t.Fatalf("unable to read golden file: %v", err)
	}
	dataJSON, err := json.MarshalIndent(data, "", "    ")
	if err != nil {
		t.Fatalf("unable to marshal to json: %v", err)
	}

	if !cmp.Equal(goldenData, dataJSON) {
		dmp := diffmatchpatch.New()
		diffs := dmp.DiffMain(string(goldenData), string(dataJSON), false)
		dmp.PatchMake()
		t.Errorf("[red] missing, [green] extra:\n%v", dmp.DiffPrettyText(diffs))
	}
}