Add post-run-command notify implementation for windows

Requires notify-send.exe: http://vaskovsky.net/notify-send

Only tested with GOOS=windows and wine, but seems to work.

README.md

@@ -165,6 +165,9 @@ example `notify` command only works on Linux with `notify-send` and on macOS wit
 On Linux, you need to have some "test-pass" and "test-fail" icons installed in your icon theme.
 Some sample icons can be found in `contrib/notify`, and can be installed with `make install`.
 
+On Windows, you can install [notify-send.exe](https://github.com/vaskovsky/notify-send)
+but it does not support custom icons so will have to use the basic "info" and "error".
+
 ```
 gotestsum --post-run-command notify
 ```

contrib/notify/notify_windows.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"strconv"
+)
+
+func main() {
+	total := envInt("TOTAL")
+	skipped := envInt("SKIPPED")
+	failed := envInt("FAILED")
+	errors := envInt("ERRORS")
+
+	icon := "info" // Info 🛈
+	title := "Passed"
+	switch {
+	case errors > 0:
+		icon = "important" // Warning ⚠
+		title = "Errored"
+	case failed > 0:
+		icon = "error" // Error ⮾
+		title = "Failed"
+	case skipped > 0:
+		title = "Passed with skipped"
+	}
+
+	subtitle := fmt.Sprintf("%d Tests Run", total)
+	if errors > 0 {
+		subtitle += fmt.Sprintf(", %d Errored", errors)
+	}
+	if failed > 0 {
+		subtitle += fmt.Sprintf(", %d Failed", failed)
+	}
+	if skipped > 0 {
+		subtitle += fmt.Sprintf(", %d Skipped", skipped)
+	}
+
+	args := []string{
+		"-i", icon,
+		title,
+		subtitle,
+	}
+	log.Printf("notify-send %#v", args)
+	err := exec.Command("notify-send.exe", args...).Run()
+	if err != nil {
+		log.Fatalf("Failed to exec: %v", err)
+	}
+}
+
+func envInt(name string) int {
+	val := os.Getenv("TESTS_" + name)
+	n, err := strconv.Atoi(val)
+	if err != nil {
+		return 0
+	}
+	return n
+}