t.js

var t = require('tap')
if (process.argv[2] === 'child') {
  t.test('parent', function (t) {
    return t.test('child', function (t) {
      return t.test('grandchild', function (t) {
        t.plan(1)
        t.fail('this is fine')
      })
    })
  })
} else {
  t.spawn(process.execPath, [__filename, 'child'])
}

test-output-buffered.tap

TAP version 13
not ok 1 - ./t.js child {
    not ok 1 - parent {
        not ok 1 - child {
            not ok 1 - grandchild {
                1..1
                not ok 1 - this is fine
                  ---
                  at:
                    line: 7
                    column: 11
                    file: t.js
                    type: global
                  stack: |
                    t.js:7:11
                    t.js:5:16
                    t.js:4:14
                    Object.<anonymous> (t.js:3:5)
                    run (bootstrap_node.js:420:7)
                    startup (bootstrap_node.js:139:9)
                    bootstrap_node.js:535:3
                  source: |
                    t.fail('this is fine')
                  ...
                # failed 1 of 1 tests
            }
            
            1..1
            # failed 1 of 1 tests
        }
        
        1..1
        # failed 1 of 1 tests
    }
    
    1..1
    # failed 1 of 1 tests
    # time=28.926ms
}

1..1
# failed 1 of 1 tests
# time=224.879ms

test-output-unbuffered.tap

TAP version 13
# Subtest: ./t.js child
    # Subtest: parent
        # Subtest: child
            # Subtest: grandchild
                1..1
                not ok 1 - this is fine
                  ---
                  at:
                    line: 7
                    column: 11
                    file: t.js
                    type: global
                  stack: |
                    t.js:7:11
                    t.js:5:16
                    t.js:4:14
                    Object.<anonymous> (t.js:3:5)
                    run (bootstrap_node.js:420:7)
                    startup (bootstrap_node.js:139:9)
                    bootstrap_node.js:535:3
                  source: |
                    t.fail('this is fine')
                  ...
                # failed 1 of 1 tests
            not ok 1 - grandchild # time=11.306ms
              ---
              at:
                line: 5
                column: 16
                file: t.js
                type: global
              results:
                plan:
                  start: 1
                  end: 1
                count: 1
                pass: 0
                ok: false
                fail: 1
                time: 11.306
              source: |
                return t.test('grandchild', function (t) {
              ...
            
            1..1
            # failed 1 of 1 tests
        not ok 1 - child # time=17.557ms
          ---
          at:
            line: 4
            column: 14
            file: t.js
            type: global
          results:
            plan:
              start: 1
              end: 1
            count: 1
            pass: 0
            ok: false
            fail: 1
            time: 17.557
          source: |
            return t.test('child', function (t) {
          ...
        
        1..1
        # failed 1 of 1 tests
    not ok 1 - parent # time=26.16ms
      ---
      at:
        line: 3
        column: 5
        file: t.js
      results:
        plan:
          start: 1
          end: 1
        count: 1
        pass: 0
        ok: false
        fail: 1
        time: 26.16
      source: |
        t.test('parent', function (t) {
      ...
    
    1..1
    # failed 1 of 1 tests
    # time=38.015ms
not ok 1 - ./t.js child # time=329.134ms
  ---
  at:
    line: 12
    column: 5
    file: t.js
  results:
    ok: false
    count: 1
    pass: 0
    fail: 1
    bailout: false
    todo: 0
    skip: 0
    plan:
      start: 1
      end: 1
      skipAll: false
      skipReason: ''
      comment: ''
  exitCode: 1
  command: /usr/local/bin/node
  arguments:
    - /Users/isaacs/dev/js/tap/t.js
    - child
  source: |
    t.spawn(process.execPath, [__filename, 'child'])
  ...

1..1
# failed 1 of 1 tests
# time=345.955ms