How to stub a static function in an abstract class | typescript

Question

Im having a real trouble testing this function Client.read.pk(string).sk(string). I created this class to ease the process of working with dynamoDB's sdk, yet when i want to unit test this method im just cant seem to stab it! thank you so much for the help!

Code:

export abstract class Client {
  static read = {
    pk: (pk: string) => {
      return {
        sk: async (sk: string) => {
          return await new DocumentClient()
            .get({
              TableName: "TodoApp",
              Key: {
                PK: pk,
                SK: sk,
              },
            })
            .promise();
        },
      };
    },
  };
}

Answer 1

Since Sinon doesn't support stub standalone function and class constructor(DocumentClient class) imported from a module, you need to use link seams. we will be using proxyquire to construct our seams.

E.g.

Client.ts:

import { DocumentClient } from 'aws-sdk/clients/dynamodb';

export abstract class Client {
  static read = {
    pk: (pk: string) => {
      return {
        sk: async (sk: string) => {
          return await new DocumentClient()
            .get({
              TableName: 'TodoApp',
              Key: {
                PK: pk,
                SK: sk,
              },
            })
            .promise();
        },
      };
    },
  };
}

Client.test.ts:

import proxyquire from 'proxyquire';
import sinon from 'sinon';

describe('68430781', () => {
  it('should pass', async () => {
    const documentClientInstanceStub = {
      get: sinon.stub().returnsThis(),
      promise: sinon.stub().resolves('mocked data'),
    };
    const DocumentClientStub = sinon.stub().callsFake(() => documentClientInstanceStub);
    const { Client } = proxyquire('./Client', {
      'aws-sdk/clients/dynamodb': { DocumentClient: DocumentClientStub },
    });
    const actual = await Client.read.pk('a').sk('b');
    sinon.assert.match(actual, 'mocked data');
    sinon.assert.calledOnce(DocumentClientStub);
    sinon.assert.calledWithExactly(documentClientInstanceStub.get, {
      TableName: 'TodoApp',
      Key: {
        PK: 'a',
        SK: 'b',
      },
    });
    sinon.assert.calledOnce(documentClientInstanceStub.promise);
  });
});

unit test result:

  68430781
    ✓ should pass (435ms)


  1 passing (439ms)

-----------|---------|----------|---------|---------|-------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------|---------|----------|---------|---------|-------------------
All files  |     100 |      100 |     100 |     100 |                   
 Client.ts |     100 |      100 |     100 |     100 |                   
-----------|---------|----------|---------|---------|-------------------