diff --git a/lib/colors.test.js b/lib/colors.test.js
index 89de15be..8bad5a1a 100644
--- a/lib/colors.test.js
+++ b/lib/colors.test.js
@@ -1,8 +1,7 @@
 'use strict'
 
 const { test } = require('tap')
-const getColorizerPrivate = require('./colors')
-const { colorizerFactory: getColorizerPublic } = require('../index')
+const getColorizer = require('./colors')
 
 const testDefaultColorizer = getColorizer => async t => {
   const colorizer = getColorizer()
@@ -122,9 +121,12 @@ const testCustomColoringColorizer = getColorizer => async t => {
   t.equal(colorized, '\u001B[37mUSERLVL\u001B[39m')
 }
 
-test('returns default colorizer - private export', testDefaultColorizer(getColorizerPrivate))
-test('returns default colorizer - public export', testDefaultColorizer(getColorizerPublic))
-test('returns colorizing colorizer - private export', testColoringColorizer(getColorizerPrivate))
-test('returns colorizing colorizer - public export', testColoringColorizer(getColorizerPublic))
-test('returns custom colorizing colorizer - private export', testCustomColoringColorizer(getColorizerPrivate))
-test('returns custom colorizing colorizer - public export', testCustomColoringColorizer(getColorizerPublic))
+test('returns default colorizer - private export', testDefaultColorizer(getColorizer))
+test('returns colorizing colorizer - private export', testColoringColorizer(getColorizer))
+test('returns custom colorizing colorizer - private export', testCustomColoringColorizer(getColorizer))
+
+test('custom props defaults to standard levels', async t => {
+  const colorizer = getColorizer(true, [], true)
+  const colorized = colorizer('info')
+  t.equal(colorized, '\u001B[37mINFO\u001B[39m')
+})
diff --git a/lib/utils/build-safe-sonic-boom.test.js b/lib/utils/build-safe-sonic-boom.test.js
index 6510bb8b..235393af 100644
--- a/lib/utils/build-safe-sonic-boom.test.js
+++ b/lib/utils/build-safe-sonic-boom.test.js
@@ -45,3 +45,42 @@ tap.test('should stream.write works when error code is not "EPIPE"', async t =>
   const dataFile = fs.readFileSync(dest)
   t.equal(dataFile.toString(), 'will work')
 })
+
+tap.test('cover setupOnExit', async t => {
+  t.plan(3)
+  const { fd, dest } = file()
+  const stream = buildSafeSonicBoom({ sync: false, fd, mkdir: true })
+
+  t.teardown(() => rimraf(dest, noop))
+
+  stream.on('error', () => t.pass('error emitted'))
+  stream.emit('error', 'fake error description')
+
+  t.ok(stream.write('will work'))
+
+  await watchFileCreated(dest)
+
+  const dataFile = fs.readFileSync(dest)
+  t.equal(dataFile.toString(), 'will work')
+})
+
+function watchFileCreated (filename) {
+  return new Promise((resolve, reject) => {
+    const TIMEOUT = 2000
+    const INTERVAL = 100
+    const threshold = TIMEOUT / INTERVAL
+    let counter = 0
+    const interval = setInterval(() => {
+      // On some CI runs file is created but not filled
+      if (fs.existsSync(filename) && fs.statSync(filename).size !== 0) {
+        clearInterval(interval)
+        resolve()
+      } else if (counter <= threshold) {
+        counter++
+      } else {
+        clearInterval(interval)
+        reject(new Error(`${filename} was not created.`))
+      }
+    }, INTERVAL)
+  })
+}
diff --git a/lib/utils/delete-log-property.js b/lib/utils/delete-log-property.js
index 7cc68350..502fcee4 100644
--- a/lib/utils/delete-log-property.js
+++ b/lib/utils/delete-log-property.js
@@ -21,6 +21,7 @@ function deleteLogProperty (log, property) {
 
   log = getPropertyValue(log, props)
 
+  /* istanbul ignore else */
   if (log !== null && typeof log === 'object' && Object.prototype.hasOwnProperty.call(log, propToDelete)) {
     delete log[propToDelete]
   }
diff --git a/lib/utils/format-time.test.js b/lib/utils/format-time.test.js
index e0e70122..be7399a9 100644
--- a/lib/utils/format-time.test.js
+++ b/lib/utils/format-time.test.js
@@ -14,6 +14,12 @@ tap.test('passes through epoch if `translateTime` is `false`', async t => {
   t.equal(formattedTime, epochMS)
 })
 
+tap.test('passes through epoch if date is invalid', async t => {
+  const input = 'this is not a date'
+  const formattedTime = formatTime(input, true)
+  t.equal(formattedTime, input)
+})
+
 tap.test('translates epoch milliseconds if `translateTime` is `true`', async t => {
   const formattedTime = formatTime(epochMS, true)
   t.equal(formattedTime, '17:30:00.000')
diff --git a/lib/utils/handle-custom-levels-names-opts.js b/lib/utils/handle-custom-levels-names-opts.js
index 2bbf724c..0c0257e2 100644
--- a/lib/utils/handle-custom-levels-names-opts.js
+++ b/lib/utils/handle-custom-levels-names-opts.js
@@ -21,14 +21,14 @@ function handleCustomLevelsNamesOpts (cLevels) {
     return cLevels
       .split(',')
       .reduce((agg, value, idx) => {
-        const [levelName, levelIdx = idx] = value.split(':')
-        agg[levelName.toLowerCase()] = levelIdx
+        const [levelName, levelNum = idx] = value.split(':')
+        agg[levelName.toLowerCase()] = levelNum
         return agg
       }, {})
   } else if (Object.prototype.toString.call(cLevels) === '[object Object]') {
     return Object
       .keys(cLevels)
-      .reduce((agg, levelName, idx) => {
+      .reduce((agg, levelName) => {
         agg[levelName.toLowerCase()] = cLevels[levelName]
         return agg
       }, {})
diff --git a/lib/utils/handle-custom-levels-names-opts.test.js b/lib/utils/handle-custom-levels-names-opts.test.js
index 489e3cf1..cdc89103 100644
--- a/lib/utils/handle-custom-levels-names-opts.test.js
+++ b/lib/utils/handle-custom-levels-names-opts.test.js
@@ -3,6 +3,11 @@
 const tap = require('tap')
 const handleCustomLevelsNamesOpts = require('./handle-custom-levels-names-opts')
 
+tap.test('returns a empty object `{}` for undefined parameter', async t => {
+  const handledCustomLevelNames = handleCustomLevelsNamesOpts()
+  t.same(handledCustomLevelNames, {})
+})
+
 tap.test('returns a empty object `{}` for unknown parameter', async t => {
   const handledCustomLevelNames = handleCustomLevelsNamesOpts(123)
   t.same(handledCustomLevelNames, {})
@@ -29,3 +34,11 @@ tap.test('returns a filled object for object parameter', async t => {
     error: 35
   })
 })
+
+tap.test('defaults missing level num to first index', async t => {
+  const result = handleCustomLevelsNamesOpts('ok:10,info')
+  t.same(result, {
+    ok: 10,
+    info: 1
+  })
+})
diff --git a/lib/utils/handle-custom-levels-opts.js b/lib/utils/handle-custom-levels-opts.js
index 099acad9..33931da1 100644
--- a/lib/utils/handle-custom-levels-opts.js
+++ b/lib/utils/handle-custom-levels-opts.js
@@ -21,15 +21,15 @@ function handleCustomLevelsOpts (cLevels) {
     return cLevels
       .split(',')
       .reduce((agg, value, idx) => {
-        const [levelName, levelIdx = idx] = value.split(':')
-        agg[levelIdx] = levelName.toUpperCase()
+        const [levelName, levelNum = idx] = value.split(':')
+        agg[levelNum] = levelName.toUpperCase()
         return agg
       },
       { default: 'USERLVL' })
   } else if (Object.prototype.toString.call(cLevels) === '[object Object]') {
     return Object
       .keys(cLevels)
-      .reduce((agg, levelName, idx) => {
+      .reduce((agg, levelName) => {
         agg[cLevels[levelName]] = levelName.toUpperCase()
         return agg
       }, { default: 'USERLVL' })
diff --git a/lib/utils/handle-custom-levels-opts.test.js b/lib/utils/handle-custom-levels-opts.test.js
index fae50a53..3f4f8f19 100644
--- a/lib/utils/handle-custom-levels-opts.test.js
+++ b/lib/utils/handle-custom-levels-opts.test.js
@@ -3,6 +3,11 @@
 const tap = require('tap')
 const handleCustomLevelsOpts = require('./handle-custom-levels-opts')
 
+tap.test('returns a empty object `{}` for undefined parameter', async t => {
+  const handledCustomLevel = handleCustomLevelsOpts()
+  t.same(handledCustomLevel, {})
+})
+
 tap.test('returns a empty object `{}` for unknown parameter', async t => {
   const handledCustomLevel = handleCustomLevelsOpts(123)
   t.same(handledCustomLevel, {})
@@ -31,3 +36,12 @@ tap.test('returns a filled object for object parameter', async t => {
     default: 'USERLVL'
   })
 })
+
+tap.test('defaults missing level num to first index', async t => {
+  const result = handleCustomLevelsOpts('ok:10,info')
+  t.same(result, {
+    10: 'OK',
+    1: 'INFO',
+    default: 'USERLVL'
+  })
+})
diff --git a/lib/utils/prettify-error-log.js b/lib/utils/prettify-error-log.js
index 24b34933..1e636b66 100644
--- a/lib/utils/prettify-error-log.js
+++ b/lib/utils/prettify-error-log.js
@@ -28,9 +28,9 @@ const prettifyObject = require('./prettify-object')
  * @param {string[]} [input.errorProperties] A set of specific error object
  * properties, that are not the value of `messageKey`, `type`, or `stack`, to
  * include in the prettified result. The first entry in the list may be `'*'`
- * to indicate that all sibiling properties should be prettified. Default: `[]`.
+ * to indicate that all sibling properties should be prettified. Default: `[]`.
  *
- * @returns {string} A sring that represents the prettified error log.
+ * @returns {string} A string that represents the prettified error log.
  */
 function prettifyErrorLog ({
   log,
diff --git a/lib/utils/prettify-error-log.test.js b/lib/utils/prettify-error-log.test.js
index d2363f6f..5d0f7db1 100644
--- a/lib/utils/prettify-error-log.test.js
+++ b/lib/utils/prettify-error-log.test.js
@@ -20,3 +20,42 @@ tap.test('returns string with custom eol', async t => {
   const str = prettifyErrorLog({ log: err, eol: '\r\n' })
   t.ok(str.startsWith('    Error: Something went wrong\r\n'))
 })
+
+tap.test('errorProperties', t => {
+  t.test('excludes all for wildcard', async t => {
+    const err = Error('boom')
+    err.foo = 'foo'
+    const str = prettifyErrorLog({ log: err, errorProperties: ['*'] })
+    t.ok(str.startsWith('    Error: boom'))
+    t.equal(str.includes('foo: "foo"'), false)
+  })
+
+  t.test('excludes only selected properties', async t => {
+    const err = Error('boom')
+    err.foo = 'foo'
+    const str = prettifyErrorLog({ log: err, errorProperties: ['foo'] })
+    t.ok(str.startsWith('    Error: boom'))
+    t.equal(str.includes('foo: foo'), true)
+  })
+
+  t.test('ignores specified properties if not present', async t => {
+    const err = Error('boom')
+    err.foo = 'foo'
+    const str = prettifyErrorLog({ log: err, errorProperties: ['foo', 'bar'] })
+    t.ok(str.startsWith('    Error: boom'))
+    t.equal(str.includes('foo: foo'), true)
+    t.equal(str.includes('bar'), false)
+  })
+
+  t.test('processes nested objects', async t => {
+    const err = Error('boom')
+    err.foo = { bar: 'bar', message: 'included' }
+    const str = prettifyErrorLog({ log: err, errorProperties: ['foo'] })
+    t.ok(str.startsWith('    Error: boom'))
+    t.equal(str.includes('foo: {'), true)
+    t.equal(str.includes('bar: "bar"'), true)
+    t.equal(str.includes('message: "included"'), true)
+  })
+
+  t.end()
+})
diff --git a/lib/utils/prettify-level.test.js b/lib/utils/prettify-level.test.js
index 438cbe8a..e127da10 100644
--- a/lib/utils/prettify-level.test.js
+++ b/lib/utils/prettify-level.test.js
@@ -25,3 +25,15 @@ tap.test('returns colorized value for color colorizer', async t => {
   const colorized = prettifyLevel({ log, colorizer })
   t.equal(colorized, '\u001B[32mINFO\u001B[39m')
 })
+
+tap.test('passes output through provided prettifier', async t => {
+  const log = {
+    level: 30
+  }
+  const colorized = prettifyLevel({ log, prettifier })
+  t.equal(colorized, 'modified')
+
+  function prettifier () {
+    return 'modified'
+  }
+})
diff --git a/lib/utils/prettify-metadata.test.js b/lib/utils/prettify-metadata.test.js
index a1342fb7..e665db0e 100644
--- a/lib/utils/prettify-metadata.test.js
+++ b/lib/utils/prettify-metadata.test.js
@@ -82,3 +82,25 @@ tap.test('works with all four present', async t => {
   const str = prettifyMetadata({ log: { name: 'foo', pid: '1234', hostname: 'bar', caller: 'baz' } })
   t.equal(str, '(foo/1234 on bar) <baz>')
 })
+
+tap.test('uses prettifiers from passed prettifiers object', async t => {
+  const prettifiers = {
+    name (input) {
+      return input.toUpperCase()
+    },
+    pid (input) {
+      return input + '__'
+    },
+    hostname (input) {
+      return input.toUpperCase()
+    },
+    caller (input) {
+      return input.toUpperCase()
+    }
+  }
+  const str = prettifyMetadata({
+    log: { pid: '1234', hostname: 'bar', caller: 'baz', name: 'joe' },
+    prettifiers
+  })
+  t.equal(str, '(JOE/1234__ on BAR) <BAZ>')
+})
diff --git a/lib/utils/prettify-object.js b/lib/utils/prettify-object.js
index 0b36949d..acee463f 100644
--- a/lib/utils/prettify-object.js
+++ b/lib/utils/prettify-object.js
@@ -49,6 +49,7 @@ function prettifyObject ({
 }) {
   const keysToIgnore = [].concat(skipKeys)
 
+  /* istanbul ignore else */
   if (excludeLoggerKeys === true) Array.prototype.push.apply(keysToIgnore, LOGGER_KEYS)
 
   let result = ''
@@ -71,6 +72,7 @@ function prettifyObject ({
 
   if (singleLine) {
     // Stringify the entire object as a single JSON line
+    /* istanbul ignore else */
     if (Object.keys(plain).length > 0) {
       result += colorizer.greyMessage(stringifySafe(plain))
     }
diff --git a/lib/utils/prettify-object.test.js b/lib/utils/prettify-object.test.js
index 7d67d912..a3492403 100644
--- a/lib/utils/prettify-object.test.js
+++ b/lib/utils/prettify-object.test.js
@@ -49,3 +49,54 @@ tap.test('works with error props', async t => {
   t.ok(str.includes('     "message": "Something went wrong",'))
   t.ok(str.includes('         Error: Something went wrong'))
 })
+
+tap.test('customPrettifiers gets applied', async t => {
+  const customPrettifiers = {
+    foo: v => v.toUpperCase()
+  }
+  const str = prettifyObject({ input: { foo: 'foo' }, customPrettifiers })
+  t.equal(str.startsWith('    foo: FOO'), true)
+})
+
+tap.test('skips lines omitted by customPrettifiers', async t => {
+  const customPrettifiers = {
+    foo: () => { return undefined }
+  }
+  const str = prettifyObject({ input: { foo: 'foo', bar: 'bar' }, customPrettifiers })
+  t.equal(str.includes('bar: "bar"'), true)
+  t.equal(str.includes('foo: "foo"'), false)
+})
+
+tap.test('joined lines omits starting eol', async t => {
+  const str = prettifyObject({
+    input: { msg: 'doing work', calls: ['step 1', 'step 2', 'step 3'], level: 30 },
+    ident: '',
+    customPrettifiers: {
+      calls: val => '\n' + val.map(it => '  ' + it).join('\n')
+    }
+  })
+  t.equal(str, [
+    'msg: "doing work"',
+    'calls:',
+    '  step 1',
+    '  step 2',
+    '  step 3',
+    ''
+  ].join('\n'))
+})
+
+tap.test('errors skips prettifiers', async t => {
+  const customPrettifiers = {
+    err: () => { return 'is_err' }
+  }
+  const str = prettifyObject({ input: { err: Error('boom') }, customPrettifiers })
+  t.equal(str.includes('err: is_err'), true)
+})
+
+tap.test('errors skips prettifying if no lines are present', async t => {
+  const customPrettifiers = {
+    err: () => { return undefined }
+  }
+  const str = prettifyObject({ input: { err: Error('boom') }, customPrettifiers })
+  t.equal(str, '')
+})
diff --git a/lib/utils/prettify-time.test.js b/lib/utils/prettify-time.test.js
index 5a3cc504..1b3e55e5 100644
--- a/lib/utils/prettify-time.test.js
+++ b/lib/utils/prettify-time.test.js
@@ -100,3 +100,13 @@ tap.test('works with epoch as a number or string', (t) => {
   t.same(asNumber, '[17:35:28.992]')
   t.same(invalid, '[2 days ago]')
 })
+
+tap.test('uses custom prettifier', async t => {
+  const str = prettifyTime({
+    log: { time: 0 },
+    prettifier () {
+      return 'done'
+    }
+  })
+  t.equal(str, 'done')
+})
diff --git a/package.json b/package.json
index ab9e9190..941148c0 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,8 @@
     "lint": "standard | snazzy",
     "test": "tap",
     "test-types": "tsc && tsd",
-    "test:watch": "tap --no-coverage-report -w"
+    "test:watch": "tap --no-coverage-report -w",
+    "test:report": "tap --coverage-report=html"
   },
   "repository": {
     "type": "git",