Class Message

be('2').message('error').toUnlawfulString(2) === 'error'
be('2').message('error').message().toUnlawfulString(2) === "expected: '2', actual: 2."

Nested case

const r = equal({
  a: 2,
  b: {
    c: '2',
    d: be('d').message('errr')
  },
  // placeholder: `:expected:` `:actual:`
  c: be('xxxx').message(':expected: :actual: error .c')
}).message('error equal')

expect(r.toUnlawfulString({ a: 2, x: '22', b: { c: '2', d: 'd' } })).toBe(
  'error equal'
)
expect(r.toUnlawfulString({ a: 2, c: 'xxxx', b: { c: '2', d: 'd' } })).toBe(
  ''
)
expect(r.toUnlawfulString({ a: 2, c: 'xxxw', b: { c: '2', d: 'd' } })).toBe(
  "c: '2' 'xxxw' error .c"
)
expect(
  r.toUnlawfulString({ a: 2, c: 'xxxx', b: { c: '2', d: 'dd' } })
).toBe("b['d']: errr")