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0.0.2 • Public • Published

Test Context Builder

In integration testing, it's sometime necessary to build a context (usually database state) that involves setting up many objects. Test Context Builder lets you define a context and load it, or define another context on top of it.

For example, let's say you need to test a money transfer operation between 2 accounts. You need the accounts, the users who own the account and the banks. You can define test context like this.

TestContext.define('base', () => {
  let ctx = {};
  ctx.bank = { id: 1, name: 'Localtown bank' };
  ctx.user = { id: 1, name: 'Bob', bankId: ctx.bank.id };
  ctx.userAccount1 = { id: 1, name: 'Checking', userId: ctx.user.id };
  ctx.userAccount2 = { id: 2, name: 'Saving', userId: ctx.user.id };
  return ctx;
describe('transfer money to same user', function() {
  beforeEach(function() {
    return dbCleaner.clean().then(() => {
      return tc.load('base');
  it('transfer from account1 to account2', function() {
    transfer(tc.context.user.account1, tc.context.user.account2);
    // write your expectation

That's good for testing transfer between 2 accounts that belongs to the same user. Now, let's say you want to test transfer between 2 accounts from 2 different users. We can reuse the base context and just add one more user.

TestContext.define('user2', ['base'], (globalCtx) => {
  let ctx = {};
  ctx.user2 = { id: 2, name: 'Bob', bankId: globalCtx.bank.id };
  ctx.user2Account1 = { id: 3, name: 'Checking', userId: ctx.user2.id };
  ctx.user2Account2 = { id: 4, name: 'Saving', userId: ctx.user2.id };
  return ctx;

The second argument of define can be an array of dependencies. So in the above example, user2 context depends on base context. The objects of the context that has been defined is accessible through globalCtx (the first arg of the function passed to the define function). So in this case we can set user2 bankId to the already defined bank object in the base context.

You can define multiple dependencies, and load the predefined test contexts having the same dependency. The dependencies will only be loaded once.

tc.load(['base', 'user2']);

In that example, it will load base first and then user2. It will see that user2 depends on base but because base is already loaded, it will just load user2. So technically you can do this in reverse order and it will still work the same.

tc.load(['user2', 'base']);
// or just load 'user2', which will also load 'base'

Use for building database test context

You can use test-context-builder with db-fabricator. Here is an example of the above case with db-fabricator.

TestContext.define('base', () => {
  let ctx = {};
  ctx.bank = Fabricator.fabricate('bank');
  ctx.user = Fabricator.fabricate('user', { bankId: ctx.bank.then(b => b.bankId) });
  return ctx;


$ npm install test-context-builder



$ tsc

Running Test

Install ts-node to run the test without compiling to js first.

$ npm install -g ts-node

Run all tests

$ mocha --compilers ts:ts-node/register test/*






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npm i test-context-builder

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  • reynardh