TcUnit can be downloaded as either a pre-compiled library or as source code. For a tutorial on how you install TcUnit from either a downloaded library or from source read the introduction user guide. The libraries are compatible with TwinCAT 3.1.4020.0 or newer.
TcUnit-Runner can be downloaded as either a pre-compiled MSI-package or as source code. For a tutorial on how you install TcUnit-Runner from an MSI-package, read the TcUnit-Runner manual.
All releases can be downloaded from the official TcUnit release site or TcUnit-Runner release site.