feat(noco-docs): Added docs for unit tests

packages/noco-docs/content/en/engineering/unit-test.md

@@ -0,0 +1,159 @@
+---
+title: "Unit Test"
+description: "How to write unit tests"
+position: 3300
+category: "Engineering"
+menuTitle: "Unit Test"
+---
+
+## Key points
+
+- We use [Mocha](https://mochajs.org/) as our test runner and [chai](https://www.chaijs.com/) as our assertion library.
+- We use [Supertest](https://www.npmjs.com/package/supertest) to test our API endpoints.
+- All individual unit tests are independent of each other. We don't use any shared state between tests.
+- Test environment also includes `sakila` database and any change on `sakila` by a test is reverted before running other tests.
+- While running unit tests, it tries to connect to mysql server running on `localhost:3306` with username `root` and password `password`(which can be configured) and if not found, it will use `sqlite` as a fallback, hence no requirement of any sql server to run tests.
+
+## Walk through of writing a unit test
+
+We will create an `Table` test suite as an example.
+
+### Describing test suite
+
+Create `Table` test suite by using `describe` function of mocha.
+
+```typescript
+export default function () {
+  describe('Table', tableTests);
+}
+```
+
+### Configure test
+
+We will configure `beforeEach` which is called before each test is executed. We will use `init` function from `nocodb/packages/tests/unit/init/index.ts`, which is a helper function which configures the test environment(i.e resetting state, etc.).
+
+`init` does the following things -
+
+- It initializes a `Noco` instance(reused in all tests).
+- Restores `meta` and `sakila` database to its initial state.
+- Creates the root user.
+- Returns `context` which has `auth token` for the created user, node server instance(`app`), and `dbConfig`.
+
+We will use `createProject` and `createProject` factories to create a project and a table.
+
+```typescript
+let context;
+
+beforeEach(async function () {
+  context = await init();
+
+  project = await createProject(context);
+  table = await createTable(context, project);
+});
+```
+
+### Test case
+
+We will use `it` function to create a test case. We will use `supertest` to make a request to the server. We use `expect`(`chai`) to assert the response.
+
+```typescript
+it('Get table list', async function () {
+  const response = await request(context.app)
+    .get(`/api/v1/db/meta/projects/${project.id}/tables`)
+    .set('xc-auth', context.token)
+    .send({})
+    .expect(200);
+
+  expect(response.body.list).to.be.an('array').not.empty;
+});
+```
+
+### Integrating the new test suite
+
+We create a new file `table.test.ts` in `packages/nocodb/tests/unit/rest/tests` directory.
+
+```typescript
+import 'mocha';
+import request from 'supertest';
+import init from '../../init';
+import { createTable, getAllTables } from '../../factory/table';
+import { createProject } from '../../factory/project';
+import { defaultColumns } from '../../factory/column';
+import Model from '../../../../src/lib/models/Model';
+import { expect } from 'chai';
+
+function tableTest() {
+  let context;
+  let project;
+  let table;
+
+  beforeEach(async function () {
+    context = await init();
+
+    project = await createProject(context);
+    table = await createTable(context, project);
+  });
+
+  it('Get table list', async function () {
+    const response = await request(context.app)
+      .get(`/api/v1/db/meta/projects/${project.id}/tables`)
+      .set('xc-auth', context.token)
+      .send({})
+      .expect(200);
+
+    expect(response.body.list).to.be.an('array').not.empty;
+  });
+}
+
+export default function () {
+  describe('Table', tableTests);
+}
+```
+
+We can then import the `Table` test suite to `Rest` test suite in `packages/nocodb/tests/unit/rest/index.test.ts` file(`Rest` test suite is imported in the root test suite file which is `packages/nocodb/tests/unit/index.test.ts`).
+
+## Running test
+
+To run tests, run `npm run test:unit` in `packages/nocodb` directory.
+
+> NOTE: We can also run individual test by using `.only` in `describe` or `it` function and the running the test command.
+
+```typescript
+it.only('Get table list', async () => {
+```
+
+## Folder structure
+
+The root folder for unit tests is `packages/tests/unit`
+
+- `rest` folder contains all the test suites for rest apis.
+- `model` folder contains all the test suites for models.
+- `factory` folder contains all the helper functions to create test data.
+- `init` folder contains helper functions to configure test environment.
+- `index.test.ts` is the root test suite file which imports all the test suites.
+- `TestDbMngr.ts` is a helper class to manage test databases (i.e. creating, dropping, etc.).
+
+## Patterns to follow
+
+- **Factories**
+  - Use factories for create/update/delete data. No data should be directly create/updated/deleted in the test.
+  - While writing a factory make sure that it can be used with as less parameters as possible and use default values for other parameters.
+  - Use named parameters for factories.
+
+  ``` typescript
+    createUser({ email, password})
+  ```
+
+  - Use one file per factory.
+
+## Using sakila db
+
+To use sakila db use `createSakilaProject` from `factory/project` to create a project. This project will be seeded with `sakila` tables.
+
+## Configurations
+
+- For Mysql db configuration, use the following environment variables to configure.
+  - `DB_USER` : mysql username
+  - `DB_PASSWORD` : mysql password
+  - `DB_HOST` : mysql host
+  - `DB_PORT` : mysql port