test_runner: fix it concurrency

Author: MoLow

lib/internal/test_runner/test.js

@@ -1,12 +1,11 @@
 'use strict';
 const {
   ArrayPrototypePush,
-  ArrayPrototypeReduce,
   ArrayPrototypeShift,
   ArrayPrototypeUnshift,
   FunctionPrototype,
   Number,
-  PromiseResolve,
+  PromiseAll,
   ReflectApply,
   SafeMap,
 } = primordials;
@@ -470,10 +469,7 @@ class Suite extends Test {
     this.parent.activeSubtests++;
     this.startTime = hrtime();
     const subtests = this.skipped ? [] : this.subtests;
-    await ArrayPrototypeReduce(subtests, async (prev, subtest) => {
-      await prev;
-      await subtest.run();
-    }, PromiseResolve());
+    await PromiseAll(ArrayPrototypeMap(subtests, (subtests) => subtests.start()));
     this.pass();
     this.postRun();
   }