diff --git a/src/workerd/io/worker-entrypoint.c++ b/src/workerd/io/worker-entrypoint.c++
index 00a822234d8..78a25827030 100644
--- a/src/workerd/io/worker-entrypoint.c++
+++ b/src/workerd/io/worker-entrypoint.c++
@@ -8,6 +8,7 @@
 #include <workerd/util/sentry.h>
 #include <workerd/api/global-scope.h>
 #include <workerd/util/own-util.h>
+#include <workerd/util/thread-scopes.h>
 
 namespace workerd {
 
@@ -181,7 +182,14 @@ kj::Promise<void> WorkerEntrypoint::request(
       failOpenClient = context.getHttpClientNoChecks(IoContext::NEXT_CLIENT_CHANNEL, false,
                                                      kj::mv(cfBlobJson));
     }
-    waitUntilTasks.add(incomingRequest->drain().attach(kj::mv(incomingRequest)));
+    auto promise = incomingRequest->drain().attach(kj::mv(incomingRequest));
+    if (isPredictableModeForTest()) {
+      promise = promise.then([worker = kj::atomicAddRef(context.getWorker())]() {
+        auto lock = worker->getIsolate().getApiIsolate().lock();
+        lock->requestGcForTesting();
+      });
+    }
+    waitUntilTasks.add(kj::mv(promise));
   })).then([this]() -> kj::Promise<void> {
     // Now that the IoContext is dropped (unless it had waitUntil()s), we can finish proxying
     // without pinning it or the isolate into memory.
@@ -349,12 +357,22 @@ kj::Promise<WorkerInterface::ScheduledResult> WorkerEntrypoint::runScheduled(
         lock.getExportedHandler(entrypointName, context.getActor()));
   }));
 
-  return incomingRequest->finishScheduled().then([&context](bool completed) mutable {
+  auto promise = incomingRequest->finishScheduled().then([&context](bool completed) mutable {
     return WorkerInterface::ScheduledResult {
       .retry = context.shouldRetryScheduled(),
       .outcome = completed ? context.waitUntilStatus() : EventOutcome::EXCEEDED_CPU
     };
   }).attach(kj::mv(incomingRequest));
+
+  if (isPredictableModeForTest()) {
+    promise = promise.then([worker = kj::atomicAddRef(context.getWorker())](auto res) {
+      auto lock = worker->getIsolate().getApiIsolate().lock();
+      lock->requestGcForTesting();
+      return res;
+    });
+  }
+
+  return promise;
 }
 
 kj::Promise<WorkerInterface::AlarmResult> WorkerEntrypoint::runAlarm(
@@ -368,7 +386,7 @@ kj::Promise<WorkerInterface::AlarmResult> WorkerEntrypoint::runAlarm(
   //alarm() should only work with actors
   auto& actor = KJ_REQUIRE_NONNULL(context.getActor());
 
-  return actor.dedupAlarm(scheduledTime,
+  auto promise = actor.dedupAlarm(scheduledTime,
       [this,&context,scheduledTime,incomingRequest = kj::mv(incomingRequest)]() mutable
       -> kj::Promise<WorkerInterface::AlarmResult> {
     incomingRequest->delivered();
@@ -395,6 +413,16 @@ kj::Promise<WorkerInterface::AlarmResult> WorkerEntrypoint::runAlarm(
       }));
     });
   });
+
+  if (isPredictableModeForTest()) {
+    promise = promise.then([worker = kj::atomicAddRef(context.getWorker())](auto res) {
+      auto lock = worker->getIsolate().getApiIsolate().lock();
+      lock->requestGcForTesting();
+      return res;
+    });
+  }
+
+  return promise;
 }
 
 kj::Promise<WorkerInterface::CustomEvent::Result>
@@ -403,7 +431,18 @@ kj::Promise<WorkerInterface::CustomEvent::Result>
                                 "customEvent() can only be called once"));
   this->incomingRequest = nullptr;
 
-  return event->run(kj::mv(incomingRequest), entrypointName).attach(kj::mv(event));
+  auto& context = incomingRequest->getContext();
+  auto worker = kj::atomicAddRef(context.getWorker());
+  auto promise = event->run(kj::mv(incomingRequest), entrypointName).attach(kj::mv(event));
+
+  if (isPredictableModeForTest()) {
+    promise = promise.then([worker = kj::mv(worker)](auto res) {
+      auto lock = worker->getIsolate().getApiIsolate().lock();
+      lock->requestGcForTesting();
+      return res;
+    });
+  }
+  return promise;
 }
 
 } // namespace workerd
diff --git a/src/workerd/jsg/jsg.c++ b/src/workerd/jsg/jsg.c++
index e5dacc57bcd..2ca84d5a9a7 100644
--- a/src/workerd/jsg/jsg.c++
+++ b/src/workerd/jsg/jsg.c++
@@ -5,6 +5,7 @@
 #include "jsg.h"
 #include "setup.h"
 #include <execinfo.h>
+#include <workerd/util/thread-scopes.h>
 
 namespace workerd::jsg {
 
@@ -149,6 +150,15 @@ void Lock::setLoggerCallback(kj::Function<Logger>&& logger) {
   IsolateBase::from(v8Isolate).setLoggerCallback({}, kj::mv(logger));
 }
 
+void Lock::requestGcForTesting() const {
+  if (!isPredictableModeForTest()) {
+    KJ_LOG(ERROR, "Test GC used while not in a test");
+    return;
+  }
+  v8Isolate->RequestGarbageCollectionForTesting(
+    v8::Isolate::GarbageCollectionType::kFullGarbageCollection);
+}
+
 Name Lock::newSymbol(kj::StringPtr symbol) {
   return Name(*this, v8::Symbol::New(v8Isolate, v8StrIntern(v8Isolate, symbol)));
 }
diff --git a/src/workerd/jsg/jsg.h b/src/workerd/jsg/jsg.h
index 56ddeca68e0..fe0c42c72d8 100644
--- a/src/workerd/jsg/jsg.h
+++ b/src/workerd/jsg/jsg.h
@@ -1906,6 +1906,7 @@ class Lock {
 
   // ---------------------------------------------------------------------------
   // Name/Symbol stuff
+
   Name newSymbol(kj::StringPtr symbol);
   // Creates a Name encapsulating a new unique v8::Symbol.
 
@@ -1970,6 +1971,14 @@ class Lock {
   using Logger = void(Lock&, kj::StringPtr);
   void setLoggerCallback(kj::Function<Logger>&& logger);
 
+  // ---------------------------------------------------------------------------
+  // Misc. Stuff
+
+  void requestGcForTesting() const;
+  // Sends an immediate request for full GC, this function is to ONLY be used in testing, otherwise
+  // it will throw. If a need for a minor GC is needed look at the call in jsg.c++ and the
+  // implementation in setup.c++. Use responsibly.
+
 private:
   friend class IsolateBase;
   template <typename TypeWrapper>