Adding Unit Test for Reducer in loklak search

Ngrx/store components are an integral part of the loklak search. All the components are dependent on how the data is received from the reducers. Reducer is like a client-side database which stores up all the data received from the API response. It is responsible for changing the state of the application. Reducers also supplies data to the Angular components from the central Store. If correct data is not received by the components, the application would crash. Therefore, we need to test if the reducer is storing the data in a correct way and changes the state of the application as expected.

Reducer also stores the current state properties which are fetched from the APIs. We need to check if reducers store the data in a correct way and if the data is received from the reducer when called from the angular components.

In this blog, I would explain how to build up different components for unit testing reducers.

Reducer to test

This reducer is used for store the data from suggest.json API from the loklak server.The data received from the server is further classified into three properties which can be used by the components to show up auto- suggestions related to current search query.

  • metadata: – This property stores the metadata from API suggestion response.
  • entities: – This property stores the array of suggestions corresponding to the particular query received from the server.
  • valid: – This is a boolean which keeps a check if the suggestions are valid or not.

We also have two actions corresponding to this reducer. These actions, when called, changes the state properties which , further, supplies data to the components in a more classified manner. Moreover, state properties also causes change in the UI of the component according to the action dispatched.

  • SUGGEST_COMPLETE_SUCCESS: – This action is called when the data is received successfully from the server.
  • SUGGEST_COMPLETE_FAIL: – This action is called when the retrieving data from the server fails.

export interface State {
metadata: SuggestMetadata;
entities: SuggestResults[];
valid: boolean;
}export const initialState: State = {
metadata: null,
entities: [],
valid: true
};export function reducer(state: State = initialState, action: suggestAction.Actions): State {
switch (action.type) {
case suggestAction.ActionTypes.SUGGEST_COMPLETE_SUCCESS: {
const suggestResponse = action.payload;return {
metadata: suggestResponse.suggest_metadata,
entities: suggestResponse.queries,
valid: true
}case suggestAction.ActionTypes.SUGGEST_COMPLETE_FAIL: {
return Object.assign({}, state, {
valid: false
}default: {
return state;

Unit tests for reducers

  • Import all the actions, reducers and mocks

import * as fromSuggestionResponse from ‘./suggest-response’;
import * as suggestAction from ‘../actions/suggest’;
import { SuggestResponse } from ‘../models/api-suggest’;
import { MockSuggestResponse } from ‘../shared/mocks/suggestResponse.mock’;


  • Next, we are going to test if the undefined action doesn’t a cause change in the state and returns the initial state properties. We will be creating an action by const action = {} as any;  and call the reducer by const result = fromSuggestionResponse.reducer(undefined, action);. Now we will be making assertions with expect() block to check if the result is equal to initialState and all the initial state properties are returned

describe(‘SuggestReducer’, () => {
describe(‘undefined action’, () => {
it(‘should return the default state’, () => {
const action = {} as any;const result = fromSuggestionResponse.reducer(undefined, action);


  • Now, we are going to test SUGGEST_COMPLETE_SUCCESS and SUGGEST_COMPLETE_FAIL action and check if reducers change only the assigned state properties corresponding to the action in a correct way.  Here, we will be creating action as assigned to the const action variable in the code below. Our next step would be to create a new state object with expected new state properties as assigned to variable const expectedResult below. Now, we would be calling reducer and make an assertion if the individual state properties of the result returned from the reducer (by calling reducer) is equal to the state properties of the expectedResult (Mock state result created to test).

describe(‘SUGGEST_COMPLETE_SUCCESS’, () => {
it(‘should add suggest response to the state’, () => {
const ResponseAction = new suggestAction.SuggestCompleteSuccessAction(MockSuggestResponse);
const expectedResult: fromSuggestionResponse.State = {
metadata: MockSuggestResponse.suggest_metadata,
entities: MockSuggestResponse.queries,
valid: true
};const result = fromSuggestionResponse.reducer(fromSuggestionResponse.initialState, ResponseAction);
});describe(‘SUGGEST_COMPLETE_FAIL’, () => {
it(‘should set valid to true’, () => {
const action = new suggestAction.SuggestCompleteFailAction();
const result = fromSuggestionResponse.reducer(fromSuggestionResponse.initialState, action);expect(result.valid).toBe(false);


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