Is there a way to debug JS unit tests for smart contracts? I use VS Code for development, and when I try to run a Mocha debugger it complains that artifacts is not defined. I briefly looked at truffle code, it looks like it adds artifacts, contract and some other global js variables when it runs the unit tests. Is there a way for me to add those explicitly in the JS unit test file so I could debug that unit test file?

2 Answers 2


Your lucky day (had to solve this few days ago):

See that you have truffle-core locally in your project. If not, do:

npm install truffle-core

Then use a configuration similar to this: ( Debug -> Open Configurations )

    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
            "type": "node",
            "request": "launch",
            "name": "truffle test (debugable)",
            "cwd": "${workspaceFolder}",
            "program": "${workspaceFolder}\\node_modules/truffle-core/cli.js",
            "args": [


Or add a new one (simple "node" launch, then edit it)

If your code does not spawn another node process (brings trouble which are essentially an node.js bug), you should be good.

  • 2
    Since truffle-core has been deprecated. Install truffle instead. Also the program path would now look like this: ${workspaceFolder}\\node_modules/truffle/build/cli.bundled.js
    – Saeb Amini
    Jan 11, 2019 at 1:36

The accepted solution above can also be used to start the debugger from command line and debug in node inspector (in Chrome dev tools):

npm install truffle-core
node --inspect-brk ./node_modules/truffle-core/cli.js test test/test_to_debug.js

UPDATE: truffle-core https://github.com/trufflesuite/truffle-core

⚠️ This repo is deprecated ⚠️ Truffle has moved all modules to a monorepo at trufflesuite/truffle. See you over there!

node --inspect-brk ./node_modules/truffle/build/cli.bundled.js test test/test_to_debug.js

Now open the debugger:

  • Open chrome://inspect page and click the "Open dedicated DevTools for Node" link
  • The cli.js file should be opened with the execution paused on the first line
  • Add the test sources into the inspector: click the "Filesystem" on the left and then "Add folder to workspace".
  • Browse to the folder with tests and add it.
  • Open the file with the test to debug and set the breakpoint, continue the execution until it reaches the breakpoint
  • Now you can step through your test, inspect variables, etc

Related links:

Truffle - Debugging unit tests

Truffle - Launching "truffle test" from JS code (debugging)

How can I debug a truffle JS unit test with vscode?

how can I run a truffle test in a debugger?

Debugging Node.js Apps

  • HINT: I'm using CMD + P to jump to file. At first not all files are loaded, using debugger statement in the code... Apr 4, 2018 at 18:12

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