new file mode 100644
--- /dev/null
+++ b/devtools/shared/tests/unit/test_sprintfjs.js
@@ -0,0 +1,113 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/**
+ * This unit test checks that our string formatter works with different patterns and
+ * arguments.
+ * Initially copied from unit tests at https://github.com/alexei/sprintf.js
+ */
+
+const {sprintf} = require("devtools/shared/sprintfjs/sprintf");
+const PI = 3.141592653589793;
+
+function run_test() {
+ // Simple patterns
+ equal("%", sprintf("%%"));
+ equal("10", sprintf("%b", 2));
+ equal("A", sprintf("%c", 65));
+ equal("2", sprintf("%d", 2));
+ equal("2", sprintf("%i", 2));
+ equal("2", sprintf("%d", "2"));
+ equal("2", sprintf("%i", "2"));
+ equal("{\"foo\":\"bar\"}", sprintf("%j", {foo: "bar"}));
+ equal("[\"foo\",\"bar\"]", sprintf("%j", ["foo", "bar"]));
+ equal("2e+0", sprintf("%e", 2));
+ equal("2", sprintf("%u", 2));
+ equal("4294967294", sprintf("%u", -2));
+ equal("2.2", sprintf("%f", 2.2));
+ equal("3.141592653589793", sprintf("%g", PI));
+ equal("10", sprintf("%o", 8));
+ equal("%s", sprintf("%s", "%s"));
+ equal("ff", sprintf("%x", 255));
+ equal("FF", sprintf("%X", 255));
+ equal("Polly wants a cracker",
+ sprintf("%2$s %3$s a %1$s", "cracker", "Polly", "wants"));
+ equal("Hello world!", sprintf("Hello %(who)s!", {who: "world"}));
+ equal("true", sprintf("%t", true));
+ equal("t", sprintf("%.1t", true));
+ equal("true", sprintf("%t", "true"));
+ equal("true", sprintf("%t", 1));
+ equal("false", sprintf("%t", false));
+ equal("f", sprintf("%.1t", false));
+ equal("false", sprintf("%t", ""));
+ equal("false", sprintf("%t", 0));
+
+ equal("undefined", sprintf("%T", undefined));
+ equal("null", sprintf("%T", null));
+ equal("boolean", sprintf("%T", true));
+ equal("number", sprintf("%T", 42));
+ equal("string", sprintf("%T", "This is a string"));
+ equal("function", sprintf("%T", Math.log));
+ equal("array", sprintf("%T", [1, 2, 3]));
+ equal("object", sprintf("%T", {foo: "bar"}));
+
+ equal("regexp", sprintf("%T", /<("[^"]*"|"[^"]*"|[^"">])*>/));
+
+ equal("true", sprintf("%v", true));
+ equal("42", sprintf("%v", 42));
+ equal("This is a string", sprintf("%v", "This is a string"));
+ equal("1,2,3", sprintf("%v", [1, 2, 3]));
+ equal("[object Object]", sprintf("%v", {foo: "bar"}));
+ equal("/<(\"[^\"]*\"|'[^']*'|[^'\">])*>/",
+ sprintf("%v", /<("[^"]*"|'[^']*'|[^'">])*>/));
+
+ // sign
+ equal("2", sprintf("%d", 2));
+ equal("-2", sprintf("%d", -2));
+ equal("+2", sprintf("%+d", 2));
+ equal("-2", sprintf("%+d", -2));
+ equal("2", sprintf("%i", 2));
+ equal("-2", sprintf("%i", -2));
+ equal("+2", sprintf("%+i", 2));
+ equal("-2", sprintf("%+i", -2));
+ equal("2.2", sprintf("%f", 2.2));
+ equal("-2.2", sprintf("%f", -2.2));
+ equal("+2.2", sprintf("%+f", 2.2));
+ equal("-2.2", sprintf("%+f", -2.2));
+ equal("-2.3", sprintf("%+.1f", -2.34));
+ equal("-0.0", sprintf("%+.1f", -0.01));
+ equal("3.14159", sprintf("%.6g", PI));
+ equal("3.14", sprintf("%.3g", PI));
+ equal("3", sprintf("%.1g", PI));
+ equal("-000000123", sprintf("%+010d", -123));
+ equal("______-123", sprintf("%+'_10d", -123));
+ equal("-234.34 123.2", sprintf("%f %f", -234.34, 123.2));
+
+ // padding
+ equal("-0002", sprintf("%05d", -2));
+ equal("-0002", sprintf("%05i", -2));
+ equal(" <", sprintf("%5s", "<"));
+ equal("0000<", sprintf("%05s", "<"));
+ equal("____<", sprintf("%'_5s", "<"));
+ equal("> ", sprintf("%-5s", ">"));
+ equal(">0000", sprintf("%0-5s", ">"));
+ equal(">____", sprintf("%'_-5s", ">"));
+ equal("xxxxxx", sprintf("%5s", "xxxxxx"));
+ equal("1234", sprintf("%02u", 1234));
+ equal(" -10.235", sprintf("%8.3f", -10.23456));
+ equal("-12.34 xxx", sprintf("%f %s", -12.34, "xxx"));
+ equal("{\n \"foo\": \"bar\"\n}", sprintf("%2j", {foo: "bar"}));
+ equal("[\n \"foo\",\n \"bar\"\n]", sprintf("%2j", ["foo", "bar"]));
+
+ // precision
+ equal("2.3", sprintf("%.1f", 2.345));
+ equal("xxxxx", sprintf("%5.5s", "xxxxxx"));
+ equal(" x", sprintf("%5.1s", "xxxxxx"));
+
+ equal("foobar", sprintf("%s", function () {
+ return "foobar";
+ }));
+}