refactor: unit test runner communicates using TCP socket (#4336)

Rewrites "cli/js/unit_test_runner.ts" to communicate with spawned subprocesses 
using TCP socket.

* Rewrite "Deno.runTests()" by factoring out testing logic to private "TestApi" 
  class. "TestApi" implements "AsyncIterator" that yields "TestEvent"s, 
  which is an interface for different types of event occuring during running
  tests.

* Add "reporter" argument to "Deno.runTests()" to allow users to provide custom
  reporting mechanism for tests. It's represented by "TestReporter" interface,
  that implements hook functions for each type of "TestEvent". If "reporter"
  is not provided then default console reporting is used (via 
  "ConsoleReporter").

* Change how "unit_test_runner" communicates with spawned suprocesses. Instead
  of parsing text data from child's stdout, a TCP socket is created and used
  for communication. "unit_test_runner" can run in either "master" or "worker"
  mode. Former is responsible for test discovery and establishing needed
  permission combinations; while latter (that is spawned by "master") executes
  tests that match given permission set.

* Use "SocketReporter" that implements "TestReporter" interface to send output
  of tests to "master" process. Data is sent as stringified JSON and then
  parsed by "master" as structured data. "master" applies it's own reporting 
  logic to output tests to console (by reusing default "ConsoleReporter").

1 files changed, 3 insertions, 6 deletions

diff --git a/cli/js/tests/unit_tests.ts b/cli/js/tests/unit_tests.ts
index 9c80859d6..4cff3d1d8 100644
--- a/cli/js/tests/unit_tests.ts
+++ b/cli/js/tests/unit_tests.ts
@@ -1,7 +1,8 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
 
-// This test is executed as part of tools/test.py
-// But it can also be run manually: ./target/debug/deno cli/js/tests/unit_tests.ts
+// This test is executed as part of unit test suite.
+//
+// Test runner automatically spawns subprocesses for each required permissions combination.
 
 import "./blob_test.ts";
 import "./body_test.ts";
@@ -63,7 +64,3 @@ import "./utime_test.ts";
 import "./write_file_test.ts";
 import "./performance_test.ts";
 import "./version_test.ts";
-
-if (import.meta.main) {
-  await Deno.runTests();
-}