The Data Charmer Thoughts and notes on software development, databases, and QA

Solving testscript problems

In the previous post, we left with the realization that something was still missing to run a full test of dbdeployer with testscript. Let’s recapitulate:

  • We have solved the problem of repeating scripts with minimal variation by using templates and creating the testdata scripts on-the-fly
  • We have created custom commands and conditions, to make the test scripts more dynamic.
  • We haven’t solved the problem of initializing the testing environment with the database versions to use.
  • We also haven’t yet found a way of checking which versions are available before the test.
  • While we were looking at the testscript capabilities, there are a few things that were not clear:
    • Why do we have two types of “commands”? one as parameter in testscript.Run and another in testscript.RunMain
    • How can I use a *testing.T method (or a testing package that embeds such type) within testscript commands?

In this article, we will check all the issues, and get away with all the solutions.


Preparing the server for dbdeployer operations can be done manually or using dbdeployer itself. Either way, the operations include the creation of a few directories, and the download of the latest MySQL binaries.

Running the initialization with dbdeployer would be desirable, as it also checks implicitly that the initialization capabilities work as expected. Doing this with testscript would be tricky, because the regular tests need the environment to be ready before starting. Rather than trying to solve this chicken-and-egg problem, I decided to run the initialization using dbdeployer functions, instead of invoking it through testscript. This problem could also be solved by creating the environment with a shell script, which works well in a CI/CD action, but I wanted this test to be runnable without external prerequisites.

The main obstacle for this course of action was that most of dbdeployer command-line functions were doing their job from a Cobra signature:

package cmd
// *** this is a poor solution ***
func doSomething(cmd *cobra.Command, args []string) error {
	option1, _ := cmd.Flags().GetString("option1Name")
	option2, _ := cmd.Flags().GetString("option2Name")
	res1 := something.runSomeRequest(option1)
    res2 := something.runSomeOtherRequest(option2)
	return putThingsTogheter(res1, res2)

This means that calling such function internally would be difficult, as the options for that function are passed as command line flags. By isolating the options functions from the Cobra handling I was able at once to make the functions more testable, and to ease the addition of more functionalities.

package ops

type SomethingOptions struct {
	Option1 string
	Option2 string

func DoSomething(options SomethingOptions) error {
	res1 := something.runSomeRequest(options.Option1)
    res2:= something.runSomeOtherRequest(options.Option2)
	return putThingsTogheter(res1, res2)
package cmd
// *** this is a better solution ***
func doSomething(cmd *cobra.Command, args []string) error {
	option1, _ := cmd.Flags().GetString("option1Name")
	option2, _ := cmd.Flags().GetString("option2Name")
	return ops.DoSomething(ops.SomethingOptions{option1, option2})

Now the testing code can call the initialization functionality without having to mess with the command line. This code gets called in the TestMain function, before any real test starts.

Checking available versions

The other point related to initializing the test refers to knowing which versions are available. Since we are using templates that create a variation of each template for each MySQL version, we need to know which versions are available. Better yet, as we may be running this test in a server that contains nothing to begin with, we need to be able to download the MySQL binaries that we want to test with dbdeployer. Using a similar solution as the one seen with the initialization, we can download each version right before TestMain checks for available versions. This way, the test can run equally well in a place that contains many versions already and in a place that is empty.

Thus, two problems solved, without really using testscript, but by improving the existing code. I would file that as a gain and a positive side effect by trying to use testscript.

Types of commands

Back to testscript. In the previous post, we have used custom commands passed as parameters in testscript.Run(). These commands accept a list of arguments, and can be used without the initial exec in any script used by the current test. Such commands work well, and I used them to my satisfaction.

There are , however, other commands that are passed as arguments to testscript.RunMain(). They don’t (apparently) accept parameters, and return an integer. I was in the dark about the meaning of this type of command, until I joined a Slack channel with several experts on the topic, and I was pointed to the gofumpt project, which uses this:

// in file main.go
func main() { os.Exit(main1()) }

func main1() int {
	// ...
	// do the real work
	return 0

// in file main_test.go
 	func TestMain(m *testing.M) {
		os.Exit(testscript.RunMain(m, map[string]func() int{
			"gofumpt": main1,

Suddenly, everything is clear: the “gofumpt” command is the equivalent of compiling gofumpt and using its binary in the testscript files. In fact, if we remove the custom command and place gofumpt in the $PATH, the tests run just the same (provided that we compiled the latest version).

The advantages of this usage are:

  • No need to previous steps to compile the executable. As in the case of the initialization, we can pre-compile the executable using a CI/CD step, but the local test would depend on it, and we may be testing the wrong version if the build process was not run on the current code.
  • The test is guaranteed to run on the latest code.

The only tiny disadvantage of this approach is that, while the test result is equivalent to using the compiled executable, we are not really testing the executable, which usually is produced by an automated process. This is not a big deal, though, as the executable can be easily tested separately as part of a CI/CD task, just to make sure that we are not distributing random garbage with an attached SHA256 checksum.

This is a great improvement for my tests. I made some more code improvements, and now my main code looks like this:

func TestMain(m *testing.M) {
	// setup code here
	exitCode := testscript.RunMain(m, map[string]func() int{
		"dbdeployer": cmd.Execute,
    // clean-up code here

The main function of dbdeployer now uses the same cmd.Execute that is the basis for the testscript command “dbdeployer”.

func main() {

The tests that previously had lines like exec dbdeployer [many arguments and options] now work just as before, with the bonus that I don’t need to worry about having compiled the executable and having placed it in $PATH.

Using testscript with quicktest in commands

As a final hurdle while writing my tests, I wanted to use quicktest not only in the test code, but also in the custom commands, as they can be considered, in their own, subtests. The problem is that the signature for a custom command does not include the *testing.T parameter that is needed to create a quicktest instance.

func checkPorts(ts *testscript.TestScript, neg bool, args []string) {

There is a TestScript parameter, which allows us to run ts.Fatalf(), or ts.Check(), but we can’t do the Assert that is what makes quicktest desirable. Since the testscript.TestScript structure doesn’t export a *testing.T parameter, we need to get creative.

In the call to testscript.Run(), where we define the custom commands, we can also call a Setup function

func TestDbDeployer(t *testing.T) {
	if !common.DirExists("testdata") {
		t.Skip("no testdata found")
	// Directories in testdata are created by the setup code in TestMain
	dirs, err := filepath.Glob("testdata/*")
	if err != nil {
		t.Skip("no directories found in testdata")
	for _, dir := range dirs {
		conditionalPrint("entering TestDbDeployer/%s", dir)
		t.Run(path.Base(dir), func(t *testing.T) {
			testscript.Run(t, testscript.Params{
				Dir:       dir,
				Cmds:      customCommands(),
				Condition: customConditions,
				Setup:     dbdeployerSetup(t, dir),

Inside the Setup function we do several things. One of them is to store the *testing.T parameter as a variable:

func dbdeployerSetup(t *testing.T, dir string) func(env *testscript.Env) error {
	return func(env *testscript.Env) error {
		// more setup actions here
		env.Values["testingT"] = t

		return nil

Now, the t argument is stored inside a variable, and the testscript.TestScript structure has a public Value field, containing the map that was set during test preparation. With this setting in place, we can now create a quicktest instance inside a command:

func getTestingT(ts *testscript.TestScript) (*qt.C, error) {
	rawT := ts.Value("testingT")
	if rawT == nil {
		return nil, fmt.Errorf("error fetching T argument from setup")
	t, ok := rawT.(*testing.T)
	if !ok {
		return nil, fmt.Errorf("error converting interface{} to *testing.T")
	return qt.New(t), nil

// findErrorsInLogFile is a testscript command that finds ERROR strings inside a sandbox data directory
func findErrorsInLogFile(ts *testscript.TestScript, neg bool, args []string) {

	c, err := getTestingT(ts)
	if len(args) < 1 {
		ts.Fatalf("no sandbox path provided")
	sbDir := args[0]
	dataDir := path.Join(sbDir, "data")
	logFile := path.Join(dataDir, "msandbox.err")
	c.Assert(common.DirExists(dataDir), qt.Equals, true)

	c.Assert(common.FileExists(logFile), qt.Equals, true)

	contents, err := ioutil.ReadFile(logFile) // #nosec G304
	hasError := strings.Contains(string(contents), "ERROR")
	if neg && hasError {
		ts.Fatalf("ERRORs found in %s\n", logFile)
	if !neg && !hasError {
		ts.Fatalf("ERRORs not found in %s\n", logFile)

In the sample above we use getTestingT to extract the value of t from the ts parameter. Once we make sure that the type conversion from interface{} to *testing.T is successful, we can use such value to build a new quicktest instance and use it for assertions in the rest of the function.

Summing up

I think my exploration of testscript has been successful. There is some tuning to perform, but at the end I have an environment where I can quickly write tests and execute them easily. Compared to using shell scripts, this is a huge technological advance. In addition to the ease of writing, the tests are also easy to read and debug.

The testscript library was developed with the aim of testing the go tool itself: if you want to test a tool that reads and manipulates text (such as gofumpt), testscript is a perfect match. And even if, as in my case, the text manipulation is minimal, testscript provides an environment that allows you to reduce boilerplate and put your tools to the test quickly. Additionally, the ability of adding custom commands and conditions makes the environment very powerful.

Now I only need to go through my large collection of shell-based tests for dbdeployer, and convert them to testscript. Wish me luck.