test_runner: give the root test a harness reference

This commit replaces the 'coverage' reference inside of the Test
class with a more generic harness reference which includes
coverage. This will let the root test more easily track process
level state such as code coverage, uncaughtException handlers,
and the state of bootstrapping.

PR-URL: #46962
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

lib/internal/test_runner/harness.js

@@ -138,7 +138,7 @@ function setup(root) {
     createProcessEventHandler('unhandledRejection', root);
   const coverage = configureCoverage(root, globalOptions);
   const exitHandler = () => {
-    root.coverage = collectCoverage(root, coverage);
+    root.harness.coverage = collectCoverage(root, coverage);
     root.postRun(new ERR_TEST_FAILURE(
       'Promise resolution is still pending but the event loop has already resolved',
       kCancelledByParent));
@@ -162,6 +162,11 @@ function setup(root) {
     process.on('SIGTERM', terminationHandler);
   }
 
+  root.harness = {
+    __proto__: null,
+    bootstrapComplete: false,
+    coverage: null,
+  };
   root.startTime = hrtime();
 
   wasRootSetup.add(root);

lib/internal/test_runner/test.js

@@ -251,7 +251,7 @@ class Test extends AsyncResource {
     this.#outerSignal?.addEventListener('abort', this.#abortHandler);
 
     this.fn = fn;
-    this.coverage = null; // Configured on the root test by the test harness.
+    this.harness = null; // Configured on the root test by the test harness.
     this.mock = null;
     this.name = name;
     this.parent = parent;
@@ -637,8 +637,8 @@ class Test extends AsyncResource {
       this.reporter.diagnostic(this.nesting, kFilename, `todo ${counters.todo}`);
       this.reporter.diagnostic(this.nesting, kFilename, `duration_ms ${this.#duration()}`);
 
-      if (this.coverage) {
-        this.reporter.coverage(this.nesting, kFilename, this.coverage);
+      if (this.harness?.coverage) {
+        this.reporter.coverage(this.nesting, kFilename, this.harness.coverage);
       }
 
       this.reporter.push(null);