A tiny test "runner".

tinyTest.mjs

class TestResult {
  value: any

  constructor (value: any) {
    this.value = value
  }
}

function assert (a: any, b?: any) {
  throw new TestResult(b ? a === b : a)
}

function throws (fn: Function, error?: Error | string) {
  try {
    fn()
    throw new TestResult(false)
  } catch(e) {
    throw new TestResult(error == null ? true : error == e)
  }
}

function test (label: string, action: Function) {
  let result = false
  
  try {
    action()
  } catch (thrown) {
    if (thrown instanceof TestResult) {
      result = thrown.value
    } else {
      result = false
    }
  }
  
  console.log(` ${result ? '✓' : '×'} ${label}`)

  if (!result) console.log(`\t\t"${result}"\n`)
}

test('should pass', () => {
  const error = new Error('testable')

  assert(true)
  assert(1, 1)
  throws(() => {throw error})
  throws(() => {throw error}, error)
})

test('should fail; assert false', () => {
  assert(false)
})

test('should fail; uncaught error', () => {
  throw new Error('testing')
})