attemptGarbageCollection during and after test cases

Runs attemptGarbageCollection() after every 250 subcases, as well as
after every case.

src/common/internal/test_group.ts

@@ -31,6 +31,7 @@ import {
   stringifyPublicParamsUniquely,
 } from '../internal/query/stringify_params.js';
 import { validQueryPart } from '../internal/query/validQueryPart.js';
+import { attemptGarbageCollection } from '../util/collect_garbage.js';
 import { DeepReadonly } from '../util/types.js';
 import { assert, unreachable } from '../util/util.js';
 
@@ -598,13 +599,20 @@ class RunCaseSpecific implements RunCase {
         if (this.subcases) {
           let totalCount = 0;
           let skipCount = 0;
+          let finishedCount = 0;
 
           // If there are too many subcases in flight, starting the next subcase will register
           // `resolvePromiseBlockingSubcase` and wait until `subcaseFinishedCallback` is called.
           let subcasesInFlight = 0;
           let resolvePromiseBlockingSubcase: (() => void) | undefined = undefined;
           const subcaseFinishedCallback = () => {
             subcasesInFlight -= 1;
+
+            finishedCount++;
+            if (finishedCount % 250 == 0) {
+              attemptGarbageCollection();
+            }
+
             // If there is any subcase waiting on a previous subcase to finish,
             // unblock it now, and clear the resolve callback.
             if (resolvePromiseBlockingSubcase) {
@@ -741,6 +749,8 @@ class RunCaseSpecific implements RunCase {
       };
       logToWebSocket(JSON.stringify(msg));
     }
+
+    attemptGarbageCollection();
   }
 }