feat: useState test util (#31)

src/testUtils.js

@@ -1,3 +1,4 @@
+import { StrictDict } from './editors/utils';
 /**
  * Mocked formatMessage provided by react-intl
  */
@@ -57,3 +58,103 @@ export const mockNestedComponents = (mapping) => Object.entries(mapping).reduce(
   }),
   {},
 );
+
+/**
+ * Mock utility for working with useState in a hooks module.
+ * Expects/requires an object containing the state object in order to ensure
+ * the mock behavior works appropriately.
+ *
+ * Expected format:
+ *   hooks = { state: { <key>: (val) => React.createRef(val), ... } }
+ *
+ * Returns a utility for mocking useState and providing access to specific state values
+ * and setState methods, as well as allowing per-test configuration of useState value returns.
+ *
+ * Example usage:
+ *   // hooks.js
+ *   import * as module from './hooks';
+ *   const state = {
+ *     isOpen: (val) => React.useState(val),
+ *     hasDoors: (val) => React.useState(val),
+ *     selected: (val) => React.useState(val),
+ *   };
+ *   ...
+ *   export const exampleHook = () => {
+ *     const [isOpen, setIsOpen] = module.state.isOpen(false);
+ *     if (!isOpen) { return null; }
+ *     return { isOpen, setIsOpen };
+ *   }
+ *   ...
+ *
+ *   // hooks.test.js
+ *   import * as hooks from './hooks';
+ *   const state = new MockUseState(hooks)
+ *   ...
+ *   describe('exampleHook', () => {
+ *     beforeEach(() => { state.mock(); });
+ *     it('returns null if isOpen is default value', () => {
+ *       expect(hooks.exampleHook()).toEqual(null);
+ *     });
+ *     it('returns isOpen and setIsOpen if isOpen is not null', () => {
+ *       state.mockVal(state.keys.isOpen, true);
+ *       expect(hooks.exampleHook()).toEqual({
+ *         isOpen: true,
+ *         setIsOpen: state.setState[state.keys.isOpen],
+ *       });
+ *     });
+ *     afterEach(() => { state.restore(); });
+ *   });
+ *
+ * @param {obj} hooks - hooks module containing a 'state' object
+ */
+export class MockUseState {
+  constructor(hooks) {
+    this.hooks = hooks;
+    this.oldState = null;
+    this.setState = {};
+
+    this.mock = this.mock.bind(this);
+    this.restore = this.restore.bind(this);
+    this.mockVal = this.mockVal.bind(this);
+  }
+
+  /**
+   * @return {object} - StrictDict of state object keys
+   */
+  get keys() {
+    return StrictDict(Object.keys(this.hooks.state).reduce(
+      (obj, key) => ({ ...obj, [key]: key }),
+      {},
+    ));
+  }
+
+  /**
+   * Replace the hook module's state object with a mocked version, initialized to default values.
+   */
+  mock() {
+    this.oldState = this.hooks.state;
+    Object.keys(this.keys).forEach(key => {
+      this.hooks.state[key] = jest.fn(val => [val, this.setState[key]]);
+    });
+    this.setState = Object.keys(this.keys).reduce(
+      (obj, key) => ({ ...obj, [key]: jest.fn() }),
+      {},
+    );
+  }
+
+  /**
+   * Restore the hook module's state object to the actual code.
+   */
+  restore() {
+    this.hooks.state = this.oldState;
+  }
+
+  /**
+   * Mock the state getter associated with a single key to return a specific value one time.
+   * @param {string} key - state key (from this.keys)
+   * @param {any} val - new value to be returned by the useState call.
+   */
+  mockVal(key, val) {
+    this.hooks.state[key].mockReturnValueOnce([val, this.setState[key]]);
+  }
+}