Table Tests, Subtests & Helpers | Go Tutorial #29

Table Tests, Subtests & Helpers in Go

Go’s built-in testing package provides powerful tools to write clear, maintainable unit tests without external dependencies. This tutorial covers essential patterns including table-driven tests, subtests, and helper functions to organize and simplify your test code effectively.

Code

package mymath

import (
  "testing"
)

// Function to test
func Add(a, b int) int {
  return a + b
}

// Test helper for error reporting
func checkSum(t *testing.T, got, want int) {
  t.Helper() // Marks this function as a test helper
  if got != want {
    t.Errorf("Add() = %d; want %d", got, want)
  }
}

// Table-driven test with subtests
func TestAdd(t *testing.T) {
  tests := []struct {
    name string
    a, b int
    want int
  }{
    {"both positive", 2, 3, 5},
    {"positive and zero", 5, 0, 5},
    {"negative and positive", -1, 1, 0},
    {"both negative", -2, -3, -5},
  }

  for _, tc := range tests {
    tc := tc // capture range variable
    t.Run(tc.name, func(t *testing.T) {
      got := Add(tc.a, tc.b)
      checkSum(t, got, tc.want)
    })
  }
}

// Example of skipping a test conditionally
func TestSkipExample(t *testing.T) {
  if testing.Short() {
    t.Skip("Skipping test in short mode")
  }
  // test code here
}

// TestMain for setup and teardown
func TestMain(m *testing.M) {
  // setup code here (e.g., initialize resources)
  code := m.Run() // run tests
  // teardown code here (e.g., clean up)
  // exit with the test result code
  // os.Exit(code)
}

Key Points

• Test functions must start with Test and accept *testing.T as a parameter.
• Table-driven tests use a slice of structs to run multiple cases cleanly and consistently.
• Subtests with t.Run() provide named, isolated test cases within a single test function.
• Use t.Helper() in helper functions to improve error reporting by skipping helper frames.
• TestMain allows setup and teardown logic around all tests in a package, and t.Skip() can conditionally skip tests.