Make fixtures files template-able :)

So it can adapt to certain env (like tcp vs unix socket for docker suite)

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

integration/utils/traefikCmd_test.go

@@ -0,0 +1,89 @@
+package utils
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+var traefikBinary = "traefik"
+
+func TestRunCommand(t *testing.T) {
+	// Override exec.Command :D
+	execCommand = fakeExecCommand
+	_, output, err := RunCommand(traefikBinary, "it", "works")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if output != "it works" {
+		t.Fatalf("Expected 'it works' as output, got : %q", output)
+	}
+}
+
+func TestRunCommandError(t *testing.T) {
+	// Override exec.Command :D
+	execCommand = fakeExecCommand
+	_, output, err := RunCommand(traefikBinary, "an", "error")
+	if err == nil {
+		t.Fatalf("Expected an error, got %q", output)
+	}
+}
+
+// Helpers :)
+
+// Type implementing the io.Writer interface for analyzing output.
+type String struct {
+	value string
+}
+
+// The only function required by the io.Writer interface.  Will append
+// written data to the String.value string.
+func (s *String) Write(p []byte) (n int, err error) {
+	s.value += string(p)
+	return len(p), nil
+}
+
+// Helper function that mock the exec.Command call (and call the test binary)
+func fakeExecCommand(command string, args ...string) *exec.Cmd {
+	cs := []string{"-test.run=TestHelperProcess", "--", command}
+	cs = append(cs, args...)
+	cmd := exec.Command(os.Args[0], cs...)
+	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
+	return cmd
+}
+
+func TestHelperProcess(t *testing.T) {
+	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
+		return
+	}
+	args := os.Args
+
+	// Previous arguments are tests stuff, that looks like :
+	// /tmp/go-build970079519/…/_test/integration.test -test.run=TestHelperProcess --
+	cmd, args := args[3], args[4:]
+	// Handle the case where args[0] is dir:...
+
+	switch cmd {
+	case traefikBinary:
+		argsStr := strings.Join(args, " ")
+		switch argsStr {
+		case "an exitCode 127":
+			fmt.Fprintf(os.Stderr, "an error has occurred with exitCode 127")
+			os.Exit(127)
+		case "an error":
+			fmt.Fprintf(os.Stderr, "an error has occurred")
+			os.Exit(1)
+		case "it works":
+			fmt.Fprintf(os.Stdout, "it works")
+		default:
+			fmt.Fprintf(os.Stdout, "no arguments")
+		}
+	default:
+		fmt.Fprintf(os.Stderr, "Command %s not found.", cmd)
+		os.Exit(1)
+	}
+	// some code here to check arguments perhaps?
+	os.Exit(0)
+}