Summary - Testing

Combine table tests and helpers to write a math test.

Testing summary

The Go testing toolbox: _test.go files, TestXxx(t *testing.T), t.Errorf/t.Fatalf, table tests + t.Run, t.Helper/t.Cleanup/t.TempDir, ExampleXxx + // Output:. On the command line: -run, -v, -race, -cover.

Taking dependencies as interfaces (e.g. io.Writer, a repository interface) makes code easy to test with fakes.

A fuzz test example

A fuzz test checks a property that "must hold for every input":

func FuzzTersCevir(f *testing.F) {
    f.Add("merhaba")
    f.Fuzz(func(t *testing.T, s string) {
        if Ters(Ters(s)) != s {
            t.Errorf("çift ters %q != %q", Ters(Ters(s)), s)
        }
    })
}

Failing inputs it finds are saved under testdata/fuzz/ and also run in later ordinary tests.

Exercise Property test

Write Ters(s string) string using runes. Print whether the property Ters(Ters(s)) == s holds for all of the inputs "gopher", "çğü" and "".

Show example solution

package main

import "fmt"

func Ters(s string) string {
    r := []rune(s)
    for i, j := 0, len(r)-1; i < j; i, j = i+1, j-1 {
        r[i], r[j] = r[j], r[i]
    }
    return string(r)
}

func main() {
    hepsi := true
    for _, s := range []string{"gopher", "çğü", ""} {
        if Ters(Ters(s)) != s {
            hepsi = false
        }
    }
    fmt.Println(hepsi)
}

Test yourself

What do <code>FuzzXxx</code> tests, added in Go 1.18, do?
- Search for bugs with randomly generated inputs
- Run tests in parallel
- Measure coverage
- Run benchmarks
Show answer

Search for bugs with randomly generated inputs — go test -fuzz=FuzzParse derives new inputs from the given seeds and tries to find a panic or failing check.

Add a seed

func FuzzParse(f *testing.F) {
    f.____("42")
    f.Fuzz(func(t *testing.T, s string) { Parse(s) })
}

Show answer

func FuzzParse(f *testing.F) {
    f.Add("42")
    f.Fuzz(func(t *testing.T, s string) { Parse(s) })
}

Test kind

TestXxx

Unit test
ExampleXxx

Docs + test
BenchmarkXxx

Performance measurement
FuzzXxx

Random input

Next lesson: Benchmark function

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