🧑‍💻 Added testing package

testing/testing.go

@@ -0,0 +1,73 @@
+// The testing package contains utilities for autotests.
+package testing
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+//nolint:gochecknoglobals // сompiler global flags cannot be read from within tests
+var update = flag.Bool("update", false, "save current tests results as golden files")
+
+// GoldenEqual compares the bytes of the provided output with the contents of
+// the golden file for a exact match.
+//
+// When running go test with the -update flag, the contents of golden-files will
+// be overwritten with the provided contents of output, creating the testdata/
+// directory if it does not exist.
+//
+// See: https://youtu.be/8hQG7QlcLBk?t=749
+//
+//nolint:cyclop // no need for splitting
+func GoldenEqual(tb testing.TB, output io.Reader) {
+	tb.Helper()
+
+	workDir, err := os.Getwd()
+	if err != nil {
+		tb.Fatal("cannot get current working directory path:", err)
+	}
+
+	actual, err := io.ReadAll(output)
+	if err != nil {
+		tb.Fatal("cannot read provided data:", err)
+	}
+
+	dir := filepath.Join(workDir, "testdata")
+	file := filepath.Join(dir, tb.Name()+".golden")
+
+	//nolint:nestif // errchecks for testdata folder first, then for output
+	if *update {
+		_, err = os.Stat(dir)
+		if err != nil && !errors.Is(err, os.ErrExist) && !errors.Is(err, os.ErrNotExist) {
+			tb.Fatal("cannot create testdata folder for golden files:", err)
+		}
+
+		if errors.Is(err, os.ErrNotExist) {
+			if err = os.Mkdir(dir, os.ModePerm); err != nil {
+				tb.Fatal("cannot create testdata folder for golden files:", err)
+			}
+		}
+
+		if err = os.WriteFile(file, actual, os.ModePerm); err != nil {
+			tb.Fatal("cannot write data into golden file:", err)
+		}
+
+		tb.Skip("skipped due force updating golden file")
+
+		return
+	}
+
+	expect, err := os.ReadFile(file)
+	if err != nil {
+		tb.Fatal("cannot read golden file data:", err)
+	}
+
+	if !bytes.Equal(actual, expect) {
+		tb.Errorf("the test output does not match the contents of %s.golden file", tb.Name())
+	}
+}