refactor: preliminary cleanup of Deno.runTests() (#4237)

* refactor: preliminary cleanup of Deno.runTests()

* Change time measurement to use new Date() instead of
  performance.now(). Because there is no guarantee that tests are
  run with "--allow-hr" using new Date() guarantees higher
  precision of 1ms instead of 2ms.

* Support String type filter in "skip" and "only".

* Split "exitOnFail" into "exitOnFail" and "failFast".
  Former tells if "runTests()" should exit with code 1 on test
  failure, while latter tells if "runTests()" should stop
  running tests on first failure.

* Use "defer" to wait for unhandled promise rejection - this bit
  is funky and doesn't seem right, but for now it's just a rewrite
  from using "setTimeout". Intended to be fixed in later commits.

* Remove global "__DENO_TEST_REGISTRY", don't expose list of
  registered tests (to be addressed in follow up commits)

* Remove arbitrary slow test threshold; use uniform coloring
  instead

cli/js/testing_test.ts

@@ -0,0 +1,37 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { assertThrows, unitTest } from "./test_util.ts";
+
+unitTest(function testFnOverloading(): void {
+  // just verifying that you can use this test definition syntax
+  Deno.test("test fn overloading", (): void => {});
+});
+
+unitTest(function nameOfTestCaseCantBeEmpty(): void {
+  assertThrows(
+    () => {
+      Deno.test("", () => {});
+    },
+    Error,
+    "The name of test case can't be empty"
+  );
+  assertThrows(
+    () => {
+      Deno.test({
+        name: "",
+        fn: () => {}
+      });
+    },
+    Error,
+    "The name of test case can't be empty"
+  );
+});
+
+unitTest(function testFnCantBeAnonymous(): void {
+  assertThrows(
+    () => {
+      Deno.test(function() {});
+    },
+    Error,
+    "Test function can't be anonymous"
+  );
+});