reorg: move js runtime tests to cli/js/tests/ (#4250)

All Deno runtime test files were moved to cli/js/tests/ directory.

It makes a clear distinction that cli/js/tests/ contains code
that is run under Deno runtime as opposed to code in cli/js/ which
is used to create bundle and snapshot with "deno_typescript".

cli/js/tests/read_dir_test.ts

@@ -0,0 +1,86 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { unitTest, assert, assertEquals } from "./test_util.ts";
+
+type FileInfo = Deno.FileInfo;
+
+function assertSameContent(files: FileInfo[]): void {
+  let counter = 0;
+
+  for (const file of files) {
+    if (file.name === "subdir") {
+      assert(file.isDirectory());
+      counter++;
+    }
+
+    if (file.name === "002_hello.ts") {
+      assertEquals(file.mode!, Deno.statSync(`cli/tests/${file.name}`).mode!);
+      counter++;
+    }
+  }
+
+  assertEquals(counter, 2);
+}
+
+unitTest({ perms: { read: true } }, function readdirSyncSuccess(): void {
+  const files = Deno.readdirSync("cli/tests/");
+  assertSameContent(files);
+});
+
+unitTest({ perms: { read: false } }, function readdirSyncPerm(): void {
+  let caughtError = false;
+  try {
+    Deno.readdirSync("tests/");
+  } catch (e) {
+    caughtError = true;
+    assert(e instanceof Deno.errors.PermissionDenied);
+  }
+  assert(caughtError);
+});
+
+unitTest({ perms: { read: true } }, function readdirSyncNotDir(): void {
+  let caughtError = false;
+  let src;
+
+  try {
+    src = Deno.readdirSync("cli/tests/fixture.json");
+  } catch (err) {
+    caughtError = true;
+    assert(err instanceof Error);
+  }
+  assert(caughtError);
+  assertEquals(src, undefined);
+});
+
+unitTest({ perms: { read: true } }, function readdirSyncNotFound(): void {
+  let caughtError = false;
+  let src;
+
+  try {
+    src = Deno.readdirSync("bad_dir_name");
+  } catch (err) {
+    caughtError = true;
+    assert(err instanceof Deno.errors.NotFound);
+  }
+  assert(caughtError);
+  assertEquals(src, undefined);
+});
+
+unitTest({ perms: { read: true } }, async function readdirSuccess(): Promise<
+  void
+> {
+  const files = await Deno.readdir("cli/tests/");
+  assertSameContent(files);
+});
+
+unitTest({ perms: { read: false } }, async function readdirPerm(): Promise<
+  void
+> {
+  let caughtError = false;
+  try {
+    await Deno.readdir("tests/");
+  } catch (e) {
+    caughtError = true;
+    assert(e instanceof Deno.errors.PermissionDenied);
+  }
+  assert(caughtError);
+});