# Jest and built-in Vim features

## Set up a sandbox

    $ cd /tmp
    $ mkdir jest-and-vim
    $ cd $_
    $ npm init -y
    $ npm install --save-dev jest

## Test around

Let's add some silly tests to `index.test.js`:

    test('adds 1 + 2 to equal 3', () => {
      expect(1 + 2).toBe(3);
    });

    test('multiplies 1 * 2 to equal 3', () => {
      expect(1 * 2).toBe(3);
    });

write the file and run `jest`:

    :!npx jest
    
     FAIL  ./index.test.js
      ✓ adds 1 + 2 to equal 3 (3 ms)
      ✕ multiplies 1 * 2 to equal 3 (3 ms)
    
      ● multiplies 1 * 2 to equal 3
    
        expect(received).toBe(expected) // Object.is equality
    
        Expected: 3
        Received: 2
    
          4 | 
          5 | test('multiplies 1 * 2 to equal 3', () => {
        > 6 |   expect(1 * 2).toBe(3);
            |                 ^
          7 | });
          8 | 
    
          at Object.test (index.test.js:6:17)
    
    Test Suites: 1 failed, 1 total
    Tests:       1 failed, 1 passed, 2 total
    Snapshots:   0 total
    Time:        1.013 s
    Ran all test suites.

This is pretty nice but we may want to make it fit better in our Vim workflow. Having the failed tests listed in the quickfix window, for example, would be a nice touch, but how to get a quickfix list out of *that*?

## Simplify output

The default output of Jest is very pretty and informative but not exactly CI and CLI-friendly. [richchurcher/jest-simple-reporter](https://github.com/richchurcher/jest-simple-reporter) is an alternative reporter that outputs results in a friendlier, Unix-like, way.

Let's install it:

    $ npm install --save-dev jest-simple-reporter

tell Jest to use our simple reporter by default:

    "jest": {
      "reporters": [
        "jest-simple-reporter"
      ]
    }

and run the test again:

    :!npx jest
    
    /tmp/jest-and-vim/index.test.js:::I::adds 1 + 2 to equal 3
    /tmp/jest-and-vim/index.test.js:6:1:E:Expected: 3 Received: 2 

This is much simpler, and easier to parse for the quickfix list.

# Make errors and fix them quickly

First, let's tell Vim to run our tests with Jest:

    :setlocal makeprg=npx\ jest

and see what we have:

    :make
    (3 sur 3) : E:Expected: 3 Received: 2
    :cwindow
    ||
    || /private/tmp/jest-and-vim/index.test.js:::I::adds 1 + 2 to equal 3
    index.test.js|6 col 1| E:Expected: 3 Received: 2

OK, the good:

- only failing tests are considered as valid errors

and the bad:

- the quickfix list is noisy,
- the non-errors pollute `:cc`, `:cnext` and friends,
- the "Error" type, `E`, is not handled properly.

Fortunately, the author of jest-simple-reporter gives what we need to build a proper `&errorformat`:

    'errorformat':
        \ '%f:%l:%c:%t:%m,' .
        \ '%-G%.%#'

which we can use like this:

    :set errorformat^=%f:%l:%c:%t:%m,%-G%.%#

Translation:

* `%f` matches a filename,
* `:` matches a colon,
* `%l` matches a line number,
* `%c` matches a column,
* `%t` matches an error type (Vim recognises `E` for "error"),
* `%f` matches a message,
* `,%-G%.%#` is here to get rid of the non-matching lines.

Let's try it:

    :make
    (1 sur 1) error : Expected: 3 Received: 2
    :cwindow
    index.test.js|6 col 1 error| Expected: 3 Received: 2

Nice! We got rid of all the bad stuff. Now is the time to create a minimal compiler scrit `compiler/jest.vim`:

    if exists("current_compiler")
      finish
    endif
    let current_compiler = "jest"

    CompilerSet makeprg=npx\ jest
    CompilerSet errorformat=%f:%l:%c:%t:%m,%-G%.%#

and call it with:

    :compiler jest

so that we can do:

    :make

to run all test files or:

    :make %

to run the current test file.

## What if…

### We could run the current test file on write?

### We could run the current test with the press of a button?