Implement blackbox in Golang (#250)

* Initial release

pkg/bbutil/sortedfile_test.go

@@ -0,0 +1,66 @@
+package bbutil
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestAddLinesToSortedFile(t *testing.T) {
+
+	var tests = []struct {
+		start    string
+		add      []string
+		expected string
+	}{
+		{
+			"",
+			[]string{"one"},
+			"one\n",
+		},
+		{
+			"begin\ntwo\n",
+			[]string{"at top"},
+			"at top\nbegin\ntwo\n",
+		},
+		{
+			"begin\ntwo\n",
+			[]string{"zbottom"},
+			"begin\ntwo\nzbottom\n",
+		},
+		{
+			"begin\ntwo\n",
+			[]string{"middle"},
+			"begin\nmiddle\ntwo\n",
+		},
+	}
+
+	for i, test := range tests {
+		content := []byte(test.start)
+		tmpfile, err := ioutil.TempFile("", "example")
+		if err != nil {
+			t.Fatal(err)
+		}
+		tmpfilename := tmpfile.Name()
+		defer os.Remove(tmpfilename)
+
+		if _, err := tmpfile.Write(content); err != nil {
+			t.Fatal(err)
+		}
+		if err := tmpfile.Close(); err != nil {
+			t.Fatal(err)
+		}
+		AddLinesToSortedFile(tmpfilename, test.add...)
+		expected := test.expected
+
+		got, err := ioutil.ReadFile(tmpfilename)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if expected != string(got) {
+			t.Errorf("test %v: contents wrong:\nexpected: %q\n     got: %q", i, expected, got)
+		}
+		os.Remove(tmpfilename)
+	}
+
+}