Set up cron job to run fuzz tester (#15718)

Sets up a CircleCI workflow to run the fuzz tests with a randomly
generated seed. The workflow runs on an hourly schedule.

.circleci/config.yml

@@ -165,6 +165,21 @@ jobs:
       - *run_yarn
       - run: yarn test-build --maxWorkers=2
 
+  test_fuzz:
+    docker: *docker
+    environment: *environment
+    steps:
+      - checkout
+      - *restore_yarn_cache
+      - *run_yarn
+      - run:
+          name: Run fuzz tests
+          command: |
+            FUZZ_TEST_SEED=$RANDOM
+            echo $FUZZ_TEST_SEED
+            yarn test fuzz --maxWorkers=2
+            yarn test-prod fuzz --maxWorkers=2
+
   test_build_prod:
     docker: *docker
     environment: *environment
@@ -177,7 +192,7 @@ jobs:
 
 workflows:
   version: 2
-  build-and-test:
+  commit:
     jobs:
       - setup
       - lint:
@@ -213,3 +228,16 @@ workflows:
       - test_build_prod:
           requires:
             - build
+  hourly:
+    triggers:
+      - schedule:
+          cron: "0 * * * *"
+          filters:
+            branches:
+              only:
+                - master
+    jobs:
+      - setup
+      - fuzz_tests:
+          requires:
+            - setup

packages/react-reconciler/src/__tests__/ReactSuspenseFuzz-test.internal.js

@@ -5,8 +5,7 @@ let Scheduler;
 let ReactFeatureFlags;
 let Random;
 
-const SEED = 0;
-
+const SEED = process.env.FUZZ_TEST_SEED || 'default';
 const prettyFormatPkg = require('pretty-format');
 
 function prettyFormat(thing) {
@@ -339,6 +338,8 @@ describe('ReactSuspenseFuzz', () => {
 Failed fuzzy test case:
 
 ${prettyFormat(randomTestCase)}
+
+Random seed is ${SEED}
 `);
 
         throw e;