testing

Testing and Overrides

The following sample demonstrates using the api-layer for your tests and overriding functionality to test different conditions using the api-layer dependency injection. See the file sample.test.ts for the sample code.

Default mock implementations

When you create your API functions using createGetApi or createSetApi, you should always create a mock version as shown in the examples. This default mock should return a positive response that is a default response that can be used by your application when testing.

Creating mock implementations

ApiLayer provides a helper function called createMockFunction that can be used to easily create mock implementations to test different functionality.

Override existing APIs

You can easily override existing API functions using the overrideApi function. This will override the API in your code base during run-time so you can test different conditions.
NOTE: If you call overrideApi multiple times, the previous override will be replaced

Using callApiFunction to wrap/alter an existing API

The callApiFunction allows you to create function that you can then wrap to alter its inputs/outputs. Typically, you would wrap the return value from callApiFunction to alter it, then install it as an override. Examples have been provided in sample.test.ts to showcase its functionality. Typical usage shown below:

import { callApiFunction, overrideApi } from 'api-layer';
import { apiGetSample } from 'api';

/**
 * The override will call the original API function, but first alter its arguments before calling the original,
 * then altering its result before returning. 
 */
const override = (value: string): Promise<string> => {
  // Change the input value to manipulate the existing function
  const newValue = `${value} override`;
  return callApiFunction(apiGetSample)(newValue).then((result) => {
    // Alter the result also
    return `${result} also overridden`;
  });
}
// Install your new override
overrideApi(apiGetSample, override);

Creating an OverrideGroup

To help you managed a large number of overrides in your testing functions, you can create an instance of an OverrideGroup. This will allow you to easily override a large number of ApiFunctions quickly and then remove them when your done.

import { OverrideGroup } from 'api-layer';
import { apiGet1, apiGet2, apiGet3 } from 'api';

function override() {
  return Promise.resolve('override value');
}

const overrides = new OverrideGroup();
// Add all your overrides by chaining the requests
overrides
  .add(apiGet1, () => Promise.resolve('override1'))
  .add(apiGet2, () => Promise.resolve('override2'))
  .add(apiGet3, () => Promise.resolve('override3'));
// Do your testing work
// Now remove all the overrides at once
overrides.removeAll();