Ts all the tests (#1998)

* Convert tests to TypeScript

* Add types for tests

* Rename files to TS

* Fix up test imports

* Fix TSC errors

* Liiiint

* Add types to util method signatures

* Some more types

test-mocha/common/datetime/format_date_time.ts

@@ -0,0 +1,20 @@
+import { assert } from "chai";
+
+import formatDateTime from "../../../src/common/datetime/format_date_time";
+
+describe("formatDateTime", () => {
+  const dateObj = new Date(2017, 10, 18, 11, 12, 13, 1400);
+
+  it("Formats English date times", () => {
+    assert.strictEqual(
+      formatDateTime(dateObj, "en"),
+      "November 18, 2017, 11:12 AM"
+    );
+  });
+
+  // Node only contains intl support for english formats. This test at least ensures
+  // the fallback to a different locale
+  it("Formats other date times", () => {
+    assert.strictEqual(formatDateTime(dateObj, "fr"), "2017 M11 18 11:12");
+  });
+});