Implement blackbox in Golang (#250)

* Initial release

pkg/box/pretty_test.go

@@ -0,0 +1,35 @@
+package box
+
+import "testing"
+
+func TestPrettyCommitMessage(t *testing.T) {
+	long := "aVeryVeryLongLongLongStringStringString"
+	for i, test := range []struct {
+		data     []string
+		expected string
+	}{
+		{[]string{}, `HEADING (no files)`},
+		{[]string{"one"}, `HEADING: one`},
+		{[]string{"one", "two"}, `HEADING: one two`},
+		{[]string{"one", "two", "three"}, `HEADING: one two three`},
+		{[]string{"one", "two", "three", "four"},
+			`HEADING: one two three four`},
+		{[]string{"one", "two", "three", "four", "five"},
+			`HEADING: one two three four five`},
+		{[]string{"has spaces.txt"}, `HEADING: "has spaces.txt"`},
+		{[]string{"two\n"}, `HEADING: "twoX"(redacted)`},
+		{[]string{"smile😁eyes"}, `HEADING: smile😁eyes`},
+		{[]string{"tab\ttab", "two very long strings.txt"},
+			`HEADING: "tabXtab"(redacted) "two very long strings.txt"`},
+		{[]string{long, long, long, long},
+			"HEADING: " + long + " " + long + " " + long + " " + long + " ...    " + long + "\n    " + long + "\n    " + long + "\n    " + long + "\n"},
+	} {
+		g := PrettyCommitMessage("HEADING", test.data)
+		if g == test.expected {
+			//t.Logf("%03d: PASSED files=%q\n", i, test.data)
+			t.Logf("%03d: PASSED", i)
+		} else {
+			t.Errorf("%03d: FAILED files==%q got=(%q) wanted=(%q)\n", i, test.data, g, test.expected)
+		}
+	}
+}