text: 
  function equal (a, b) {
      if (a !== b)
          throw new Error(`${a} is not equal to ${b}`)
  }
  
  
  function deepEqual (a, b) {
      if (a.length !== b.length)
          throw new Error(`${a} is not equal to ${b}`)
  
      for (let i=0; i < a.length; i++)
          if (a[i] !== b[i])
              throw new Error(`${a} is not equal to ${b}`)
  }
  
  
  function almostEqual (actual, expected, message='') {
      if (Math.abs(actual - expected) > 1e-8)
          equal(actual, expected, message);
  }
  
  
  function notNull (value) {
      if (value === null) 
          throw new Error("value is unexpectedly null")
    
      return value
  }
  
  
  export default { almostEqual, notNull, equal, deepEqual }
  