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The testcase package provides tooling to apply BDD testing conventions.

If you use Go1.20, then due to the changes in the stdlib testing package, please upgrade testcase to version >= v0.131.0.


  • lightweight, it has no dependency, you just import testcase, no clutter
  • supports classing flattened testing style, table testing style, and nested testing style
    • nested testing style
      • allows the usage of an immutable testing subject
      • nesting visualize code complexity
      • testing context building becomes DRY
      • immutable testing subject construction forces disciplined testing conventions
      • supports also the flattened nesting where testing context branches can to a top-level function
  • DDD based testing composition
    • testing components can be defined and reused across the whole project
    • unit tests can be converted into full-fledged E2E tests for CI/CD pipelines
    • dependency injection during testing becomes a breeze to do
    • reusable testing components increase maintainability aspects
    • reusable testing components decrease required ramp-up time for writing new tests that depend on existing components
  • safe parallel testing
    • variables stored per test execution, which prevents leakage and race conditions across different tests
  • repeatable pseudo-random fixture generation for test input
  • repeatable pseudo-random test order shuffling
    • prevents implicit test dependency on ordering
    • ensures that tests can be added and removed freely without the fear of breaking other tests in the same coverage.
    • flaky tests which depend on test execution order can be noticed at development time


testcase is a powerful TDD Tooling that requires discipline and understanding of the fundamentals of testing. If you are looking for a guide that helps streamline your knowledge on the topics, then please consider reading the below-listed articles.

Official API Documentation

If you already use the framework, and you just won't pick an example, you can go directly to the API documentation that is kept in godoc format.

Getting Started / Example

Examples kept in godoc format. Every exported functionality aims to have examples provided in the official documentation.

A Basic examples:

func Test_withTestcaseT(t *testing.T) {
	tc := testcase.NewT(t, nil)
	_ = tc.Random.String()

func Test_withTestcaseSpec(t *testing.T) {
	s := testcase.NewSpec(t)
	s.Test("", func(t *testcase.T) {
		_ = tc.Random.String()

An example with scoped test variables:

package main

import (


func TestMyFunc(t *testing.T) {
	s := testcase.NewSpec(t)

	var (
		input = testcase.Let[string](s, nil)
	act := func(t *testcase.T) string {
		return MyFunc(input.Get(t))

	s.When("input is all lowercase", func(s *testcase.Spec) {
		// testing scopes without the input being defined
		// will warn the dev about the missing specification.
		input.LetValue(s, "all lowercase")

		s.Then("it is expected to ...", func(t *testcase.T) {
			t.Must.Equal("all lowercase", act(t))

	s.When("input is all upcase", func(s *testcase.Spec) {
		input.LetValue(s, "ALL UPCASE")

		s.Then("it is expected to ...", func(t *testcase.T) {
			t.Must.Equal("all upcase", act(t))


  • httpspec
    • spec module helps you create HTTP API Specs.
  • fixtures
    • fixtures module helps you create random input values for testing



testcase provides a way to express common Arrange, Act sections for the Asserts with a DRY principle in mind.

  • First, you can define your Act section with a method under test as the subject of your test specification
    • The Act section invokes the method under test with the arranged parameters.
  • Then you can build the context of the Act by Arranging the inputs later with humanly explained reasons
    • The Arrange section initializes objects and sets the value of the data that is passed to the method under test.
  • And lastly, you can define the test expected outcome in an Assert section.
    • The Assert section verifies that the action of the method under test behaves as expected.

Then adding test edge case to the testing suite becomes easier, as it will have a concrete place where it must be placed.

And if during the creation of the specification, an edge case turns out to be YAGNI, it can be noted, so visually it will be easier to see what edge case is not specified for the given subject.

The value it gives is that to build a test for a certain edge case, the required mental model size to express the context becomes smaller, as you only have to focus on one Arrange at a time, until you fully build the bigger picture.

It also implicitly visualize the required mental model of your production code by the nesting. You can read more on that in the nesting section.


On top of the DRY convention, any time you need to Arrange a common scenario about your projects domain event, you can modularize these setup blocks in a helper function.

This helps the readability of the test while keeping the need for mocks to the minimum as possible for a given test. As a side effect, integration tests can become low-hanging fruit for the project.


package mypkg_test

import (



	. "my/project/testing/pkg"

func TestMyTypeMyFunc(t *testing.T) {
	s := testcase.NewSpec(t)
	myUser := GivenWeHaveUser(s)
	// .. other givens

	myType := testcase.Let(s, func(t *testcase.T) *mypkg.MyType {
		return &mypkg.MyType{}

	s.Describe(`.MyFunc`, func(s *testcase.Spec) {
		act := func(t *testcase.T) { myType.Get(t).MyFunc(myUser.Get(t)) }

		s.Then(`edge case description`, func(t *testcase.T) {


  • The package is considered stable.
  • The package use rolling release conventions.
  • No breaking change is planned to the package exported API.
  • The package used in production development.
  • The package API is only extended if the practical use case proves its necessity.

Reference Project