Save an Apex file and Nimbus reruns the affected tests, with no terminal command and no manual trigger. Results arrive in under a second.
The usual Apex cycle is deploying to a scratch org, waiting for the deploy, running the test and reading the output. That takes minutes per iteration.
With watch mode the cycle is write, save, read the result. Nimbus detects the file change, compiles the affected class in-process and reruns the relevant tests, typically in under 200ms for a single class. Nothing is deployed.
Watch mode works from the terminal with nimbus test:watch and is built into the Dev UI, where the Watch button starts the same watcher in the browser.
Run nimbus test:watch in your project directory. Nimbus starts watching your Apex source files and reruns tests on save; results stream to the terminal as they complete.
By default, watch mode reruns tests related to the saved file. If you save AccountService.cls, Nimbus reruns test classes that reference AccountService. You can also pass an explicit pattern to restrict which tests run.
Pass --all to rerun the full suite on every change, for small projects or when you want the whole suite after every edit.
# Watch and rerun affected tests on save
nimbus test:watch
# Watch with explicit test pattern
nimbus test:watch "AccountServiceTest.*"
# Rerun all tests on every change
nimbus test:watch --all
# Watch a specific package directory
nimbus test:watch --path force-app/main/default
# Output
# Watching force-app/**/*.cls ...
# [14:23:01] AccountService.cls changed
# [14:23:01] Running AccountServiceTest... ✓ 6/6 (182ms)
# [14:23:01] Ready.Watch mode prints pass or fail per method, failure messages inline and the duration per run. Between saves it prints nothing.
In nimbus dev, the Watch button in the toolbar starts the same file watcher. Results update in the browser as tests complete.
The Dev UI adds a Watch scope dropdown the terminal does not have. In multi-package projects it restricts watching to one package path, so only tests related to that package rerun on save, which keeps reruns short in large monorepos.
The parallel workers panel appears during runs and shows each active test worker and what it's currently running. Watch respects your nimbus.test.parallel setting, so more cores mean faster reruns.
In large projects, rerunning every test on every save takes too long. Watch mode has two ways to narrow it.
Pattern scoping: pass a test pattern and only tests matching that pattern rerun on any file change. Useful when you are working in one area and do not need the full suite.
Path scoping: pass --path to restrict which source files are watched. Changes outside that path are ignored. Useful in monorepos where packages are independent.
# Only rerun AccountServiceTest on any change
nimbus test:watch "AccountServiceTest.*"
# Watch a specific directory
nimbus test:watch --path force-app/main/default/classes
# Combine: pattern + path scope
nimbus test:watch "AccountServiceTest.*" \
--path force-app/main/default
# Configure default watch settings in nimbus.properties:
# nimbus.watch.path=force-app/main/default
# nimbus.watch.pattern=AccountServiceTest.*The Nimbus extension activates watch mode when you open an Apex test class. Save any Apex file and results update in the Test Explorer sidebar: pass or fail per method, inline failure messages, coverage gutter decorations.
The Nimbus plugin adds a Watch toggle to the Nimbus tool window. Enable it, save a file, and results update in the test tree. The plugin highlights failing lines in the editor margin.
nimbus test:watch runs from any terminal without an editor plugin. Useful when pairing, in remote environments, or in editors without a Nimbus plugin.
Run nimbus dev and enable Watch in the toolbar. Results stream to the browser over WebSocket: test tree, inline failure messages, live coverage percentages. It runs alongside your editor.
Save a file and the affected tests run, with no deploy and no terminal command. Use nimbus test:watch or the Watch button in the Dev UI; both run the same watcher.