How to write unit tests

Impact Framework unit tests follow a standard format. We use the jest testing library. You can run all our existing tests by opening the project directory and running npm test. This page explains how you can add new unit tests for your plugins (or add some for our plugins if you notice a gap).

Test files

Both the IF and the project repositories include a __test__ directory. Inside, you will find subdirectory unit/lib containing directories for each plugin. Your plugin repository should also follow this structure. Inside the plugin directory you can add index.test.ts. This is where you write your unit tests. For example, here's the directory tree for our teads-curve test file:

if-unofficial-plugins
 |
 |- src
    |
    |-__tests__
        |
        |-unit
          |
          |-lib
             |
             teads-curve
                 |
                 |- index.test.ts

Setting up your test file

You will need to import your plugin so that it can be instantiated and tested. You will also need some elements from jest/globals: For example, these are the imports for our Sum plugin.

import {Sum} from '../../../../lib';
import {ERRORS} from '../../../../util/errors';
const {InputValidationError} = ERRORS;

You may require other imports for your specific set of tests.

Describe

Each method should have its own dedicated describe block.

Your unit tests should have at least two describe blocks, one to test the plugin initialization and one for execute.

describe("init", ()=> {})
describe("execute", ()=> {})

For example, here is a describe block checking that the Sum plugin initializes correctly:

describe('lib/sum: ', () => {
  describe('Sum: ', () => {
    const globalConfig = {
      'input-parameters': ['cpu/energy', 'network/energy', 'memory/energy'],
      'output-parameter': 'energy',
    };
    const sum = Sum(globalConfig);

    describe('init: ', () => {
      it('successfully initalized.', () => {
        expect(sum).toHaveProperty('metadata');
        expect(sum).toHaveProperty('execute');
      });
    });
  })
})

It

Within each describe block, each effect to be tested should have a dedicated it block.

Here's an example of a new describe block for the execute() method on the Sum plugin. The describe block indicates that we are testing effects of the execute() method. it is specific to a single outcome - in this case there are two it blocks that test that the plugin returns a specific result in the happy path and throws an exception if the user has provided invalid config data, specifically that the user-provided cpu/energy parameter is missing:

    describe('execute(): ', () => {
      it('successfully applies Sum strategy to given input.', async () => {
        expect.assertions(1);

        const expectedResult = [
          {
            duration: 3600,
            'cpu/energy': 1,
            'network/energy': 1,
            'memory/energy': 1,
            energy: 3,
            timestamp: '2021-01-01T00:00:00Z',
          },
        ];

        const result = await sum.execute([
          {
            duration: 3600,
            'cpu/energy': 1,
            'network/energy': 1,
            'memory/energy': 1,
            timestamp: '2021-01-01T00:00:00Z',
          },
        ]);

        expect(result).toStrictEqual(expectedResult);
      });

      it('throws an error on missing params in input.', async () => {
        const expectedMessage =
          'Sum: cpu/energy is missing from the input array.';

        expect.assertions(1);

        try {
          await sum.execute([
            {
              duration: 3600,
              timestamp: '2021-01-01T00:00:00Z',
            },
          ]);
        } catch (error) {
          expect(error).toStrictEqual(
            new InputValidationError(expectedMessage)
          );
        }
      });
    })

Errors

We prefer to use expect to check the errors returned from a test. We do this by writing expect in a catch block. Here's an example from our sci plugin tests:

it('throws an exception on missing functional unit data.', async () => {
  const inputs = [
    {
      timestamp: '2021-01-01T00:00:00Z',
      'operational-carbon': 0.002,
      'embodied-carbon': 0.0005,
      'functional-unit': 'requests',
      duration: 1,
    },
  ];
  expect.assertions(1);

  try {
    await sciModel.execute(inputs);
  } catch (error) {
    expect(error).toBeInstanceOf(InputValidationError);
  }
});

It is also necessary to include expect.assertions(n) for testing asynchronous code, where n is the number of assertiosn that should be tested before the test completes.

Mocks

Please try to avoid mocking data if possible. However, if it is necessary to mock (e.g. if your plugin relies on a third party credentialed API) then please make your mock data as realistic as possible (no foo, bar, baz style mock data, please).

We do have mock backends in several of our tests, and we also have a mock data generator plugin that can create realistic dummy data to your specific requirements.

Coverage

Please use jest --coverage to see a coverage report for your plugin - your unit tests should yield 100% coverage. The snippet below shows what to expect from the coverage report:

-------------------------------|---------|----------|---------|---------|-------------------
| File                        | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
| --------------------------- | ------- | -------- | ------- | ------- | ----------------- |
| All files                   | 100     | 100      | 100     | 100     |
| lib                         | 100     | 100      | 100     | 100     |
| index.ts                    | 100     | 100      | 100     | 100     |
| lib/cloud-metadata          | 100     | 100      | 100     | 100     |
| index.ts                    | 100     | 100      | 100     | 100     |
| lib/e-mem                   | 100     | 100      | 100     | 100     |
| index.ts                    | 100     | 100      | 100     | 100     |
| lib/e-net                   | 100     | 100      | 100     | 100     |
| index.ts                    | 100     | 100      | 100     | 100     |