example.for.test.factory.js

/**

Consider the language did not provide us with `.indexOf` and we had to implement it ourselves.
Given that the factory is already implemented, how easy is it to add a new case.

Mind how hoisting helps keep the higher levels above, while implementation details are below.

 */
const Should = require('should');
const SUT = require('./index-of');

describe('indexOf(stack, needle)', () => {
  
  Object.entries({
    "needle found in the end":    ["jhdskaaaD"     , "aaaD" , 5],
    "needle found in start" :     ["sdlfsamsqaeca" , "sdl"  , 0],
    "needle found in the middle": ["sdssdlfsamsqaa", "sdl"  , 3],
    "needle appears twice":       ["sdsaSDLfssSDLa", "SDL"  , 4],
    "needle contains punctuation":["eh,wtf!#$help" , "wtf!" , 2],
    "needle contains unicode":    ["sгеройDLa"     , "герой", 1],
    "needle not in stack":        ["sdssdlfsamseca", "sdlx" ,-1],
    "empty needle":               ["sddssd"        , ""     , 0],
    "empty stack":                [""              , "df"   ,-1],
    "stack is not a string":      [{}              , "df"   ,'TypeError'],
    "needle is not a string":     ["sajkhdjj"      , {}     ,'TypeError'],
  })
  .forEach(caseFactory);
  
  function caseFactory([spec, [stack, needle, expected]]) {
    describe('when ' + spec, () => {
      let found, err;
      before(() => {
        found = SUT(stack, needle);
      });
      
      if (typeof expected 'string') { 
        it(`should throw a ${expected} augmented with the passed stack and needle`, () => {
          Should(err)
            .be.instanceOf(Error)
            .with.properties({ name: expected, stack, needle });
        });
        return;
      }
      if (expected == -1) {
        it('should indicate no find by returning -1', () => {
           Should(found).eql(-1);
        });
        return;
      }
      it('should return the correct first index', () => {
         Should(found).eql(expected);
      });
    });
  }

});