IDIOMATIC GOLANG TESTS A GUIDE TO

WHY TO TEST?

TO DOCUMENT

TO ENSURE IT WORKS

TO WRITE BETTER CODE

HOW TO TEST?

package simple_calculator func Sum(a int, b int) int { return a + b }

func TestSumValid(t *testing.T) { got := Sum(2, 2) if got != 4 { t.Errorf("Sum() = %v, want %v", got, 4) } } func TestSumInvalid(t *testing.T) { // some test logic here }

$ go test -v ./ === RUN TestSumValid --- PASS: TestSumValid (0.00s) === RUN TestSumInvalid --- PASS: TestSumInvalid (0.00s) PASS ok simple_calculator 0.008s

SUB TESTS

func TestSum(t *testing.T) { t.Run("sum-valid", func(t *testing.T) { got := Sum(2, 2) if got != 4 { t.Errorf("Sum() = %v, want %v", got, 4) } }) t.Run("sum-invalid", func(t *testing.T) { // some test logic here }) }

$ go test -v ./ === RUN TestSum === RUN TestSum/sum-valid === RUN TestSum/sum-invalid --- PASS: TestSum (0.00s) --- PASS: TestSum/sum-valid (0.00s) --- PASS: TestSum/sum-invalid (0.00s) ok simple_calculator 0.008s

TABLE DRIVEN

type args struct { a int b int } type testCase struct { name string args args want int } tests := []testCase{ {"sum 2+2", args{1, 2}, 3}, }

for _, tt := range tests { t.Run(tt.name, func(t *testing.T) { got := Sum(tt.args.a, tt.args.b) if got != tt.want { t.Errorf("Sum() = %v, want %v", got, tt.want) } }) }

$ go test -v ./ === RUN TestSum === RUN TestSum/sum_2+2 --- PASS: TestSum (0.00s) --- PASS: TestSum/sum_2+2 (0.00s) ok simple_calculator 0.008s

TEXT TABLE DRIVEN TESTS ▸ Easy to add new test cases ▸ Don’t repeat same logic ▸ Easy to reproduce bugs ▸ Can be used even for one test case

func Fibonacci(n uint) uint { if n <= 1 { return n } var n2, n1 = uint(0), uint(1) for i := uint(1); i < n; i++ { n2 = n2 + n1 n1, n2 = n2, n1 } return n1 }

func TestFibonacci(t *testing.T) { tests := []struct { name string number uint want uint }{ {"10", 10, 55}, {"50", 50, 12586269025}, {"9999999999", 9999999999, 2225628016866617058}, } for _, tt := range tests { t.Run(tt.name, func(t *testing.T) { if got := Fibonacci(tt.number); got != tt.want { t.Errorf("Fibonacci() = %v, want %v", got, tt.want) } }) } }

$ go test -v ./ === RUN TestFibonacci === RUN TestFibonacci/10 === RUN TestFibonacci/50 === RUN TestFibonacci/9999999999 --- PASS: TestFibonacci (7.49s) --- PASS: TestFibonacci/10 (0.00s) --- PASS: TestFibonacci/50 (0.00s) --- PASS: TestFibonacci/9999999999 (7.49s) PASS ok simple_calculator 7.502s

FLAGS

var skipSlow = flag.Bool("skipSlow", false, "Skip slow tests")

func TestFibonacci(t *testing.T) { tests := []struct { name string number uint want uint isSlow bool }{ {"10", 10, 55, false}, {"50", 50, 12586269025, false}, {"9999999999", 9999999999, 2225628016866617058, true}, } for _, tt := range tests { t.Run(tt.name, func(t *testing.T) { if *skipSlow && tt.isSlow { t.Skipf("Skiped slow test") } if got := Fibonacci(tt.number); got != tt.want { t.Errorf("Fibonacci() = %v, want %v", got, tt.want) } }) } }

$ go test -v -skipSlow ./ === RUN TestFibonacci === RUN TestFibonacci/10 === RUN TestFibonacci/50 === RUN TestFibonacci/9999999999 --- PASS: TestFibonacci (0.00s) --- PASS: TestFibonacci/10 (0.00s) --- PASS: TestFibonacci/50 (0.00s) --- SKIP: TestFibonacci/9999999999 (0.00s) calculator_test.go:73: Skiped slow test PASS ok simple_calculator 0.008s

RACE CONDITIONS

type Item struct { Value int } func (item Item) PersistRand(n int) { rand.Seed(time.Now().UnixNano()) for i := 0; i < n; i++ { go func() { item.Value = rand.Int() }() } }

$ go test -v ./ === RUN TestItem_PersistRand === RUN TestItem_PersistRand/10 --- PASS: TestItem_PersistRand (0.00s) --- PASS: TestItem_PersistRand/10 (0.00s) PASS ok idiomatic-tests-examples/kv 0.010s

$ go test -v -race ./ === RUN TestItem_PersistRand === RUN TestItem_PersistRand/10 ================== WARNING: DATA RACE Write at 0x00c0000920c0 by goroutine 9: idiomatic-tests-examples/kv.Item.PersistRand.func1() /Users/hussani/projects/go-workspace/src/idiomatic-tests- examples/kv/storage.go:17 +0x46 Previous write at 0x00c0000920c0 by goroutine 8: idiomatic-tests-examples/kv.Item.PersistRand.func1()

FIXTURES

func TestPersistRand(t *testing.T) { data := filepath.Join( "test-fixtures", "persist-data.json.fixture" ) // Do something on test using data }

TEXT FIXTURES ▸ Use to complex string input ▸ Use to iterate on system folders ▸ Use to loads configuration , json, binary data, etc

GOLDEN FILES

func TestFetchPersist(t *testing.T) { // a table test case for _, tc := range testCases { golden := filepath.Join( "test-fixtures", tc.name + ".golden" ) expected, _ := ioutil.ReadFile(golden) if got := doSomething(tc.input); got != expected { t.Errorf("doSomething() result doesn't match golden. got %v", got) } ) }

TEXT GOLDEN FILES ▸ Use to compare complex string output ▸ Need to be updated always your output changes

SUMMARY

TEXT SUMMARY ▸ Always do tests! They are important ▸ Test using Table Driven ▸ Use flags to control some test execution ▸ Always execute tests with race flag ▸ Don’t put complex or long strings on your test file ▸ Use Fixtures & Golden files ▸ Happy testing :)

THANKS! twitter.com/hussanii