test: drain platform before unregistering isolate

Backport-PR-URL: #28005
PR-URL: #27375
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/cctest/node_test_fixture.h

@@ -107,6 +107,7 @@ class NodeTestFixture : public ::testing::Test {
   void TearDown() override {
     isolate_->Exit();
     isolate_->Dispose();
+    platform->DrainTasks(isolate_);
     platform->UnregisterIsolate(isolate_);
     isolate_ = nullptr;
   }

test/cctest/test_environment.cc

@@ -88,6 +88,19 @@ TEST_F(EnvironmentTest, MultipleEnvironmentsPerIsolate) {
   EXPECT_TRUE(called_cb_2);
 }
 
+TEST_F(EnvironmentTest, NoEnvironmentSanity) {
+  const v8::HandleScope handle_scope(isolate_);
+  v8::Local<v8::Context> context = v8::Context::New(isolate_);
+  EXPECT_EQ(node::Environment::GetCurrent(context), nullptr);
+  EXPECT_EQ(node::GetCurrentEnvironment(context), nullptr);
+  EXPECT_EQ(node::Environment::GetCurrent(isolate_), nullptr);
+
+  v8::Context::Scope context_scope(context);
+  EXPECT_EQ(node::Environment::GetCurrent(context), nullptr);
+  EXPECT_EQ(node::GetCurrentEnvironment(context), nullptr);
+  EXPECT_EQ(node::Environment::GetCurrent(isolate_), nullptr);
+}
+
 TEST_F(EnvironmentTest, NonNodeJSContext) {
   const v8::HandleScope handle_scope(isolate_);
   const Argv argv;