:sparkles: (Go) mocking

Go/mocking/mocking.go

···
+package main
+
+import (
+    "fmt"
+    "io"
+    "os"
+    "time"
+)
+
+type Sleeper interface {
+    Sleep()
+}
+
+const (
+    finalWord = "Go!"
+    countdownStart = 3
+)
+
+func Countdown(out io.Writer, sleeper Sleeper) {
+    for i := countdownStart; i > 0; i-- {
+        fmt.Fprintln(out, i)
+        sleeper.Sleep()
+    }
+    fmt.Fprint(out, finalWord)
+}
+
+type DefaultSleeper struct {}
+
+func (d *DefaultSleeper) Sleep() {
+    time.Sleep(1 * time.Second)
+}
+
+func main() {
+    sleeper := &DefaultSleeper{}
+    Countdown(os.Stdout, sleeper)
+}

Go/mocking/mocking_test.go

···
+package main
+
+import (
+    "bytes"
+    "reflect"
+    "testing"
+)
+
+type SpySleeper struct {
+    Calls int
+}
+
+func (s *SpySleeper) Sleep() {
+    s.Calls++
+}
+
+type SpyCountdownOperations struct {
+    Calls []string
+}
+
+func (s *SpyCountdownOperations) Sleep() {
+    s.Calls = append(s.Calls, sleep)
+}
+
+func (s *SpyCountdownOperations) Write(p []byte) (n int, err error) {
+    s.Calls = append(s.Calls, write)
+    return
+}
+
+const write = "write"
+const sleep = "sleep"
+
+func TestCountdown(t *testing.T) {
+    t.Run("spying sleep", func(t *testing.T) {
+        buffer := &bytes.Buffer{}
+        spySleeper := &SpySleeper{}
+
+        Countdown(buffer, spySleeper)
+
+        got := buffer.String()
+        want := `3
+2
+1
+Go!`
+
+        if got != want {
+            t.Errorf("got %q want %q", got, want)
+        }
+
+        if spySleeper.Calls != 3 {
+            t.Errorf("not enough calls to sleeper, want 3 got %d", spySleeper.Calls)
+        }
+    })
+
+    t.Run("sleep before every print", func(t *testing.T) {
+        spySleepPrinter := &SpyCountdownOperations{}
+        Countdown(spySleepPrinter, spySleepPrinter)
+
+        want := []string{
+            write,
+            sleep,
+            write,
+            sleep,
+            write,
+            sleep,
+            write,
+        }
+
+        if !reflect.DeepEqual(want, spySleepPrinter.Calls) {
+            t.Errorf("wanted calls %v got %v", want, spySleepPrinter.Calls)
+        }
+    })
+}