From 09f4571fde7b958f82eef3f87a98bb7fe22259ac Mon Sep 17 00:00:00 2001
From: Marcello Lamonaca <marcello.lamonaca@gmail.com>
Date: Fri, 19 Mar 2021 15:18:20 +0100
Subject: [PATCH] Redux Tests Notes

---
 JavaScript/React/Redux Tests.md | 151 ++++++++++++++++++++++++++++++++
 1 file changed, 151 insertions(+)
 create mode 100644 JavaScript/React/Redux Tests.md

diff --git a/JavaScript/React/Redux Tests.md b/JavaScript/React/Redux Tests.md
new file mode 100644
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+# Redux Testing
+
+## Tests for Connected Components
+
+Connected components are warpped in a call to `connect`. Way of solving the problem:
+
+- Wrap component with `<Provider>`. Added benefit: new store dedicated to tests.
+- Add named export for unconncted component.
+
+In `Component.js`:
+
+```js
+export function Component(props) { /* ... */ }  // export unconnected component
+
+export default connect(mapStateToProps, mapDispatchToProps)(Component)  // default export of connected component
+```
+
+In `Component.test.js`:
+
+```js
+import React from "react";
+// import enzyme or react testing library
+
+// import mock data
+import { Component } from "path/to/Component";  // import unconnected component
+
+// factory to setup test easily
+function testHelper(args) {
+    const defaultProps = { 
+        /* default value for props in each test and required props */,
+        history = {}  // normally injected by react-router, could also import the router
+    };
+
+    const props = { ...defaultProps, ...args };
+    return mount(<Component {...props} />);  // or render if using react testing library
+}
+
+it("test description", () => {
+    const dom = testHelper();
+
+    // simulate page interation
+    dom.find("selctor").simulate("<event>");
+
+    // find changed component
+    // test expected behaviour of component
+});
+```
+
+## Tests for Action Creators
+
+```js
+import * as actions from "path/to/actionCreators";
+// import eventual action types constants
+// import mock data
+
+describe("Async Actions", () => {
+    afterEach(() => {
+        fetchMock.restore();  // init fecth mok for each test
+    });
+
+    it("test description", () => {
+        // mimic API call
+        fetchMock.mock(
+            "*",  // capture any fetch call
+            {
+                body: /* body contents */,
+                headers: { "content-type": "application/json" }
+            }
+        );
+
+        const expectedActions = [
+            { type: TYPE, /* ... */ },
+            { type: TYPE, /* ... */ }
+        ];
+
+        const store = mockStore({ data: value, ... });
+        return store.dispatch(actions.actionCreator())
+            .then(() => {
+                expect(store.getActions()).toEqual(expectedActions);
+            });
+    });
+});
+```
+
+## Tests for Reducers
+
+```js
+import reducer from "path/to/reducer";
+import * as actions from "path/to/actionCreators";
+
+it("test description", () => {
+    const initialState = /* satte before the action */;
+    const stateUpdate = /* modified state */;
+
+    const action = actions.actionCreator(stateUpdate);
+
+    const newState = reducer(initialState, action);
+
+    expect(newState.property).toEqual(actual);
+});
+```
+
+## Tests for the Store
+
+```js
+import { createStore } from "redux";
+
+import rootReducer from "path/to/rootReducer";
+import initialState from "path/to/initialState";
+import * as actions from "path/to/actionCreators";
+
+it("test description", () => {
+    const store = createStore(toorReducer, initialState);
+
+    const stateUpdate = /* modified state */;
+    const action = actions.actionCreator(stateUpdate);
+    store.dispatch(action);
+
+    const state = store.getState();
+    expect(state).toEqual(stateUpdate);
+});
+```
+
+## Tests for Thunks
+
+Thunk testing requires the mocking of:
+
+- store (using `redux-mock-store`)
+- HTTP calls (using `fetch-mock`)
+
+```js
+import thunk from "redux-thunk";
+import fetchMock from "getch-mock";
+import configureMockStore from "redux-mock-store";
+
+import * as actions from "path/to/actionCreators";
+// import eventual action types constants
+// import mock data
+
+const middleware = [thunk];  // mock middlewares
+const mockStore = configureMockStore(middleware);  // mock the store
+
+it("test description", () => {
+    const data = /* mock data */
+    const expectedAction = { type: TYPE, /* ... */ };
+
+    const actualAction = actions.actionCreator(data);
+
+    expect(actualAction).toEqual(expectedAction);
+});
+```