A simple (and assumed) example of how Jasmine works under the hood using Describe->It->Expect->EqualsTo pattern. Meant to help to understand the workings of tests rather than being accurate to Jasmine itself.

simple_and_fake_jasmine_describe_it_expect_equalsto_pattern.js

// Run the file `node simple_and_fake_jasmine_describe_it_expect_equalsto_pattern.js` from containing folder.
// Should receive 1 passing and 1 failing test (as noted by text color -> Green/Red).
// To understand: read from the call site and work backwards.

// -- Fancy console printing like tests do (no emojis yet) -- //
const printToConsole = function(text, status = 'normal', padding = false) {
  const CC = {
    Reset: '\x1b[0m',
    Underscore: '\x1b[4m',
    FgRed: '\x1b[31m',
    FgGreen: '\x1b[32m',
  };
  
  let pad = '';
  if (padding) pad = '  ';

  if (status === 'success') {
    console.log(`${pad}${CC.FgGreen}%s${CC.Reset}`, text);
  } else if (status === 'normal') {
    console.log(`${pad}${CC.Underscore}%s${CC.Reset}`, text);
  } else if (status === 'failure') {
    console.log(`${pad}${CC.FgRed}%s${CC.Reset}`, text);
  } else {
    console.log('Error calling printToConsole status');
  }
};

// -- Testing suite -- // 

// -- State of the result of the test -- //
// -- This should probably be a private internal variable inside the test module -- //
// -- but I was lazy so it just gets overwrite globally in this file. -- //
let testingStateResult = null;

const describe = function(logTitle, context) {
  printToConsole(logTitle);
  context();
  testingStateResult = null;
};

const it = function(logTitle, context) {
  context();
  printToConsole(logTitle, testingStateResult, true);
};

const expect = function(actualValue) {
  this.toEqual = (expectedValue) => { 
    const results = actualValue === expectedValue;
    if (results) {
      testingStateResult = 'success';
    } else {
      testingStateResult = 'failure';
    }
    return results;
  };
  return this;
};

// -- Function to be tested -- //
const hello = function(name) {
  return `Hello ${name}`;
};

// -- Test Examples -- //
describe(
  'hello()', 
  function() {
    // -- Successful Test -- //
    it(
      'returns a spaced concatenated string: Hello Adora',
      function() {
        expect(hello('Adora')).toEqual('Hello Adora');
      }
    );
    // -- Failing Test -- //
    it(
      'returns a spaced concatenated string: Hello Catra',
      function() {
        expect(hello('Catra')).toEqual('HelloCatra');
      }
    );
  }
);