test_runner: run global before hook after bootstrap

This commit updates top level 'before' hook logic so that the
hooks do not run before the test runner finishes bootstrapping.
This is necessary for running multiple test files in the same
process.

lib/internal/test_runner/harness.js

@@ -163,6 +163,7 @@ function setup(root) {
   const exitHandler = async () => {
     if (root.subtests.length === 0 && (root.hooks.before.length > 0 || root.hooks.after.length > 0)) {
       // Run global before/after hooks in case there are no tests
+      await root.runHook('before', root.getRunArgs());
       await root.run();
     }
     root.postRun(new ERR_TEST_FAILURE(

lib/internal/test_runner/test.js

@@ -682,8 +682,10 @@ class Test extends AsyncResource {
     if (name === 'before' || name === 'after') {
       hook.run = runOnce(hook.run, kRunOnceOptions);
     }
-    if (name === 'before' && this.startTime !== null) {
-      // Test has already started, run the hook immediately
+    // If the test has already started, run the hook immediately. Do not run
+    // top level hooks immediately though so that we have a chance to load all
+    // of the tests.
+    if (name === 'before' && this.startTime !== null && this.parent !== null) {
       PromisePrototypeThen(hook.run(this.getRunArgs()), () => {
         if (hook.error != null) {
           this.fail(hook.error);

test/fixtures/test-runner/output/global-hooks-with-no-tests.snapshot

@@ -1,5 +1,5 @@
-before
 TAP version 13
+before
 after
 1..0
 # tests 0