Fuzz tester for context

package.json

@@ -79,6 +79,7 @@
     "platform": "^1.1.0",
     "prettier": "1.8.1",
     "prop-types": "^15.6.0",
+    "random-seed": "^0.3.0",
     "rimraf": "^2.6.1",
     "rollup": "^0.51.7",
     "rollup-plugin-babel": "^2.7.1",

packages/react-reconciler/src/__tests__/ReactNewContext-test.js

@@ -9,14 +9,16 @@
 
 'use strict';
 
-let React;
+let React = require('React');
 let ReactNoop;
+let gen;
 
 describe('ReactNewContext', () => {
   beforeEach(() => {
     jest.resetModules();
     React = require('react');
     ReactNoop = require('react-noop-renderer');
+    gen = require('random-seed');
   });
 
   // function div(...children) {
@@ -303,4 +305,211 @@ describe('ReactNewContext', () => {
       span('Result: 4'),
     ]);
   });
+
+  describe('fuzz test', () => {
+    const contextKeys = ['A', 'B', 'C', 'D', 'E', 'F', 'G'];
+    const contexts = new Map(
+      contextKeys.map(key => {
+        const Context = React.createContext(0);
+        Context.displayName = 'Context' + key;
+        return [key, Context];
+      }),
+    );
+    const Fragment = React.Fragment;
+
+    const FLUSH_ALL = 'FLUSH_ALL';
+    function flushAll() {
+      return {
+        type: FLUSH_ALL,
+        toString() {
+          return `flushAll()`;
+        },
+      };
+    }
+
+    const FLUSH = 'FLUSH';
+    function flush(unitsOfWork) {
+      return {
+        type: FLUSH,
+        unitsOfWork,
+        toString() {
+          return `flush(${unitsOfWork})`;
+        },
+      };
+    }
+
+    const UPDATE = 'UPDATE';
+    function update(key, value) {
+      return {
+        type: UPDATE,
+        key,
+        value,
+        toString() {
+          return `update('${key}', ${value})`;
+        },
+      };
+    }
+
+    function randomInteger(min, max) {
+      min = Math.ceil(min);
+      max = Math.floor(max);
+      return Math.floor(Math.random() * (max - min)) + min;
+    }
+
+    function randomAction() {
+      switch (randomInteger(0, 3)) {
+        case 0:
+          return flushAll();
+        case 1:
+          return flush(randomInteger(0, 500));
+        case 2:
+          const key = contextKeys[randomInteger(0, contextKeys.length)];
+          const value = randomInteger(1, 10);
+          return update(key, value);
+        default:
+          throw new Error('Switch statement should be exhaustive');
+      }
+    }
+
+    function randomActions(n) {
+      let actions = [];
+      for (let i = 0; i < n; i++) {
+        actions.push(randomAction());
+      }
+      return actions;
+    }
+
+    class ConsumerTree extends React.Component {
+      shouldComponentUpdate() {
+        return false;
+      }
+      render() {
+        if (this.props.depth >= this.props.maxDepth) {
+          return null;
+        }
+        const consumers = [0, 1, 2].map(i => {
+          const randomKey =
+            contextKeys[this.props.rand.intBetween(0, contextKeys.length - 1)];
+          const Context = contexts.get(randomKey);
+          return Context.consume(
+            value => (
+              <Fragment>
+                <span prop={`${randomKey}:${value}`} />
+                <ConsumerTree
+                  rand={this.props.rand}
+                  depth={this.props.depth + 1}
+                  maxDepth={this.props.maxDepth}
+                />
+              </Fragment>
+            ),
+            i,
+          );
+        });
+        return consumers;
+      }
+    }
+
+    function Root(props) {
+      return contextKeys.reduceRight((children, key) => {
+        const Context = contexts.get(key);
+        const value = props.values[key];
+        return Context.provide(value, children);
+      }, <ConsumerTree rand={props.rand} depth={0} maxDepth={props.maxDepth} />);
+    }
+
+    const initialValues = contextKeys.reduce(
+      (result, key, i) => ({...result, [key]: i + 1}),
+      {},
+    );
+
+    function assertConsistentTree(expectedValues = {}) {
+      const children = ReactNoop.getChildren();
+      children.forEach(child => {
+        const text = child.prop;
+        const key = text[0];
+        const value = parseInt(text[2], 10);
+        const expectedValue = expectedValues[key];
+        if (expectedValue === undefined) {
+          // If an expected value was not explicitly passed to this function,
+          // use the first occurrence.
+          expectedValues[key] = value;
+        } else if (value !== expectedValue) {
+          throw new Error(
+            `Inconsistent value! Expected: ${key}:${expectedValue}. Actual: ${
+              text
+            }`,
+          );
+        }
+      });
+    }
+
+    function ContextSimulator(maxDepth) {
+      function simulate(seed, actions) {
+        const rand = gen.create(seed);
+        let finalExpectedValues = initialValues;
+        function updateRoot() {
+          ReactNoop.render(
+            <Root
+              maxDepth={maxDepth}
+              rand={rand}
+              values={finalExpectedValues}
+            />,
+          );
+        }
+        updateRoot();
+
+        actions.forEach(action => {
+          switch (action.type) {
+            case FLUSH_ALL:
+              ReactNoop.flush();
+              break;
+            case FLUSH:
+              ReactNoop.flushUnitsOfWork(action.unitsOfWork);
+              break;
+            case UPDATE:
+              finalExpectedValues = {
+                ...finalExpectedValues,
+                [action.key]: action.value,
+              };
+              updateRoot();
+              break;
+            default:
+              throw new Error('Switch statement should be exhaustive');
+          }
+          assertConsistentTree();
+        });
+
+        ReactNoop.flush();
+        assertConsistentTree(finalExpectedValues);
+      }
+
+      return {simulate};
+    }
+
+    it('hard-coded tests', () => {
+      const {simulate} = ContextSimulator(5);
+      simulate('randomSeed', [flush(3), update('A', 4)]);
+    });
+
+    it('generated tests', () => {
+      const {simulate} = ContextSimulator(5);
+
+      const LIMIT = 100;
+      for (let i = 0; i < LIMIT; i++) {
+        const seed = Math.random()
+          .toString(36)
+          .substr(2, 5);
+        const actions = randomActions(5);
+        try {
+          simulate(seed, actions);
+        } catch (error) {
+          console.error(`
+Context fuzz tester error! Copy and paste the following line into the test suite:
+  simulate('${seed}', ${actions.join(', ')});
+`);
+          throw error;
+        }
+      }
+    });
+  });
 });

yarn.lock

@@ -3045,7 +3045,7 @@ json-stable-stringify@^1.0.0, json-stable-stringify@^1.0.1:
   dependencies:
     jsonify "~0.0.0"
 
-json-stringify-safe@~5.0.1:
+json-stringify-safe@^5.0.1, json-stringify-safe@~5.0.1:
   version "5.0.1"
   resolved "https://registry.yarnpkg.com/json-stringify-safe/-/json-stringify-safe-5.0.1.tgz#1296a2d58fd45f19a0f6ce01d65701e2c735b6eb"
 
@@ -3811,6 +3811,12 @@ qs@~6.4.0:
   version "6.4.0"
   resolved "https://registry.yarnpkg.com/qs/-/qs-6.4.0.tgz#13e26d28ad6b0ffaa91312cd3bf708ed351e7233"
 
+random-seed@^0.3.0:
+  version "0.3.0"
+  resolved "https://registry.yarnpkg.com/random-seed/-/random-seed-0.3.0.tgz#d945f2e1f38f49e8d58913431b8bf6bb937556cd"
+  dependencies:
+    json-stringify-safe "^5.0.1"
+
 randomatic@^1.1.3:
   version "1.1.6"
   resolved "https://registry.yarnpkg.com/randomatic/-/randomatic-1.1.6.tgz#110dcabff397e9dcff7c0789ccc0a49adf1ec5bb"