added Go variant

- using homegrown approval test function

go/theatre/approval_test.go

@@ -0,0 +1,78 @@
+package theatre_test
+
+import (
+	"bytes"
+	"io/ioutil"
+	"path"
+	"strings"
+	"testing"
+)
+
+// verify runs a list of sub-tests using input data from the "testdata" subdirectory named after the current test.
+// All files with the suffix ".in.<inType>" are used as input for the test case function.
+// The name before the suffix is used as the base name for the files this function uses.
+//
+// What the function returns will be compared to the file with suffix ".approved.<outType>".
+// If its content does not match the result, or the file does not exist, the test fails and a file with suffix ".out.<outType>" is created.
+//
+// In case the function encounters an error, it can call Fatalf() on the passed test instance.
+// To verify errors as approved data, be sure to include the error in your structured data.
+//
+// This function reports problems of file access, as well as a failure if no input files were found.
+func verify(t *testing.T, inType string, outType string, testCase func(testing.TB, []byte) []byte) {
+	t.Helper()
+	datadir := path.Join("testdata", t.Name())
+	files, err := ioutil.ReadDir(datadir)
+	if err != nil {
+		t.Fatalf("could not read test directory: %v", err)
+	}
+	fullInSuffix := ".in." + inType
+	fullApprovedSuffix := ".approved." + outType
+	inputData := make(map[string][]byte)
+	approvedData := make(map[string][]byte)
+	for _, file := range files {
+		switch {
+		case file.IsDir():
+		case strings.HasSuffix(file.Name(), fullInSuffix):
+			data, err := ioutil.ReadFile(path.Join(datadir, file.Name()))
+			if err != nil {
+				t.Errorf("failed to read input file %s: %v", file.Name(), err)
+			}
+			inputData[file.Name()] = data
+		case strings.HasSuffix(file.Name(), fullApprovedSuffix):
+			data, err := ioutil.ReadFile(path.Join(datadir, file.Name()))
+			if err != nil {
+				t.Errorf("failed to read approved file %s: %v", file.Name(), err)
+			}
+			approvedData[file.Name()] = data
+		}
+	}
+	if len(inputData) == 0 {
+		t.Fatalf("no input files in %s - is this the intent?", datadir)
+	}
+	for rangedInFilename, rangedInData := range inputData {
+		inFilename := rangedInFilename
+		inData := rangedInData
+		t.Run(t.Name()+"/"+inFilename, func(t *testing.T) {
+			result := testCase(t, inData)
+
+			baseFilename := inFilename[:len(inFilename)-len(fullInSuffix)]
+			expected, hasApproved := approvedData[baseFilename+fullApprovedSuffix]
+			writeOutFile := false
+			switch {
+			case !hasApproved:
+				t.Errorf("no approved data available (file %s not available)", baseFilename+fullApprovedSuffix)
+				writeOutFile = true
+			case !bytes.Equal(expected, result):
+				t.Errorf("result does not match expectation")
+				writeOutFile = true
+			}
+			if writeOutFile {
+				err = ioutil.WriteFile(path.Join(datadir, baseFilename+".out."+outType), result, 0644)
+				if err != nil {
+					t.Errorf("failed to write output data: %v", err)
+				}
+			}
+		})
+	}
+}