What is VUnit?

VUnit is an open source unit testing framework for VHDL/SystemVerilog released under the terms of Mozilla Public License, v. 2.0. It features the functionality needed to realize continuous and automated testing of your HDL code. VUnit doesn’t replace but rather complements traditional testing methodologies by supporting a “test early and often” approach through automation.

VUnit reduces the overhead of testing by supporting automatic discovery of test benches and compilation order as well as including libraries for common verification tasks. It improves the speed of development by supporting incremental compilation and by enabling large test benches to be split up into smaller independent tests. It increases the quality of projects by enabling large regression suites to be run on a continuous integration server.

VUnit does not impose any specific verification methodology on its users. The benefits of VUnit can be enjoyed when writing tests first or last, when writing long running top level tests or short running unit tests, when using directed or constrained random testing. Often projects adopt mix of approaches for different testing needs. VUnit has been used in production environments where thousands of tests take several hours to run on powerful multi-core machines as well as in small open source projects where only a small package is tested in a few seconds.

Main Features

  • Python test suite runner that enables powerful test administration, can continue testing after fatal run-time errors (e.g. division by zero), and ensures test case independence.

  • Automatic scanning of files for tests, file dependencies, and file changes enable automatic (re)compilation and execution of test suites.

  • Can run test cases in parallel to take advantage of multi-core machines.

  • Support for running test benches with multiple generic/parameter settings.

  • Scriptable API as well as command line support.

  • Has --gui switch to launch test cases in the simulator GUI when debugging is necessary.

  • Assertion checker library that extends VHDL built-in support (assert).

  • Logging framework supporting display and file output, different log levels, visibility settings of levels and design hierarchy, output formatting and multiple loggers. Supports machine readable output formats that for example can be read by a spreadsheet.

  • Requirements trace-ability through JSON Export and test attributes.

  • Optional location preprocessor that traces log and check calls back to file and line number.

  • Outputs JUnit report files for better Jenkins integration.

  • Builds on the commonly used xUnit architecture.


VUnit depends on a number of components as listed below. Full VUnit functionality requires Python and a simulator supported by the VUnit Python test runner. However, VUnit can run with limited functionality entirely within VHDL using the VHDL test runner.


  • VHDL-93

  • VHDL-2002

  • VHDL-2008

  • Verilog

  • SystemVerilog (Support is experimental)

Operating systems

  • Windows

  • Linux

  • Mac OS X


  • Python 3.4 or higher

  • Python 2.7

    • VUnit support for Python 2.7 will end in 1 Jan 2020 when it reaches end of life.


  • Aldec Riviera-PRO

    • Tested with Riviera-PRO 2015.06, 2015.10, 2016.02, 2016.10 (x64/x86).

    • Only VHDL

  • Aldec Active-HDL

    • Tested with Active-HDL 9.3, 10.1, 10.2, 10.3 (x64/x86)

    • Only VHDL

  • Mentor Graphics ModelSim/Questa

    • Tested with 10.1 - 10.5

  • GHDL

    • Only VHDL

    • Works with versions >= 0.33

    • Tested with LLVM and mcode backends, gcc backend might work aswell.

    • Integrated support for using GTKWave to view waveforms.

  • Cadence Incisive (Experimental)

    • Community contribution by Colin Marquardt. VUnit maintainers does not have access to this simulator to verify the functionality.

    • Run incisive_vhdl_fixup.py to remove VHDL constructs that are

      not compatible with Incisive

Getting Started

There are a number of ways to get started.


Any bug reports, feature requests or questions about the usage of VUnit can be made by creating a new issue.


Notable contributors



VUnit except for OSVVM (see below) is released under the terms of Mozilla Public License, v. 2.0.

© 2014-2018 Lars Asplund, lars.anders.asplund@gmail.com.


OSVVM is redistributed with VUnit for your convenience. These files are licensed under the terms of ARTISTIC License.

© 2010 - 2017 by SynthWorks Design Inc. All rights reserved.