Implement blackbox in Golang (#250)

* Initial release

integrationTest/asserts.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/andreyvit/diff"
+)
+
+func assertFileMissing(t *testing.T, name string) {
+	t.Helper()
+	_, err := os.Stat(name)
+	if err != nil && os.IsNotExist(err) {
+		return
+	}
+	if err == nil {
+		t.Fatalf("assertFileMissing failed: %v exists", name)
+	}
+	t.Fatalf("assertFileMissing: %q: %v", name, err)
+}
+
+func assertFileExists(t *testing.T, name string) {
+	t.Helper()
+	_, err := os.Stat(name)
+	if err == nil {
+		return
+	}
+	if os.IsNotExist(err) {
+		t.Fatalf("assertFileExists failed: %v not exist", name)
+	}
+	t.Fatalf("assertFileExists: file can't be accessed: %v: %v", name, err)
+}
+
+func assertFileEmpty(t *testing.T, name string) {
+	t.Helper()
+	c, err := ioutil.ReadFile(name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(c) != 0 {
+		t.Fatalf("got=%v want=%v: %v", len(c), 0, name)
+	}
+}
+
+func assertFileContents(t *testing.T, name string, contents string) {
+	t.Helper()
+	c, err := ioutil.ReadFile(name)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if w, g := contents, string(c); w != g {
+		t.Errorf("assertFileContents(%q) mismatch (-got +want):\n%s",
+			name, diff.LineDiff(g, w))
+	}
+}
+
+func assertFilePerms(t *testing.T, name string, perms os.FileMode) {
+	t.Helper()
+	s, err := os.Stat(name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s.Mode() != perms {
+		t.Fatalf("got=%#o want=%#o: %v", s.Mode(), perms, name)
+	}
+}