foo-test.coffee

# __tests__/foo-test.coffee
describe 'hai', ->
  it 'asdf', ->
    foo = require '../foo'
    console.log foo

  it 'asdf2', ->
    foo = require '../foo'
    console.log foo

foo.coffee

# foo.coffee

module.exports = 42;

package.json

{
  "name": "test",
  "dependencies": {
    "coffee-script": "*",
    "jest-cli": "*"
  },
  "jest": {
    "scriptPreprocessor": "<rootDir>/preprocessor.js",
    "testFileExtensions": ["coffee", "js"],
    "moduleFileExtensions": ["js", "json", "coffee"]
  }
}

preprocessor.js

var coffee = require('coffee-script');

module.exports = {
  process: function(src, path) {
    // CoffeeScript files can be .coffee, .litcoffee, or .coffee.md
    if (coffee.helpers.isCoffee(path)) {
      return coffee.compile(src, {'bare': true});
    }
    return src;
  }
};