v0.21.0

Features

• Add guide for testing functions to docs site (#85) - @lkipke
• Update _brs_.mockFunction API docs to reflect new functionality (#82) - @lkipke

Fixes

• Stop double-counting tests with our Jest reporter (#86) - @lkipke

Internal

• bump y18n from 4.0.0 to 4.0.1 (#84)
• bump node-notifier from 8.0.0 to 8.0.2 (#83)