Cover code generation with tests

Add test coverage of code generation program.

internal/cmd/generatecode/main.go

@@ -313,7 +313,12 @@ func createFile(wg *sync.WaitGroup, path string, cb func(*os.File)) {
 	}()
 }
 
-func main() {
+type filesToCreate struct {
+	tupleFilename string
+	zipFilename   string
+}
+
+func createFiles(toCreate filesToCreate) {
 	tupleNames = map[int]string{
 		1:  "Unit",
 		2:  "Pair",
@@ -343,8 +348,15 @@ func main() {
 
 	var wg sync.WaitGroup
 
-	createFile(&wg, "tuple.go", writeTupleFile)
-	createFile(&wg, "zip.go", writeZipFile)
+	createFile(&wg, toCreate.tupleFilename, writeTupleFile)
+	createFile(&wg, toCreate.zipFilename, writeZipFile)
 
 	wg.Wait()
 }
+
+func main() {
+	createFiles(filesToCreate{
+		tupleFilename: "tuple.go",
+		zipFilename:   "zip.go",
+	})
+}

internal/cmd/generatecode/main_test.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestCacheB(t *testing.T) {
+	t.Parallel()
+
+	dirName, err := os.MkdirTemp("", "")
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.RemoveAll(dirName)
+
+	// Run the code to generate files and ensure it doesn't blow up.
+	createFiles(filesToCreate{
+		tupleFilename: dirName + "/tuple.go",
+		zipFilename:   dirName + "/zip.go",
+	})
+}