Engine Dev Testing

Usage

Always run with run_in_background: true and poll with TaskOutput. Playground builds take 1-5 minutes; the Bash tool's default timeout (120s) and max timeout (10 min) are both problematic for synchronous execution.

Step 1: Start the playground in the background.

Bash(command="skills/engine-dev-testing/with-playground.sh 'dagger version'", run_in_background=true)
→ returns task_id

Step 2: Poll for completion. Use TaskOutput with block: true and a reasonable timeout (60s). The script prints a heartbeat every 30s, so you'll see [playground: 30s elapsed, still running...] while it builds.

TaskOutput(task_id=<id>, block=true, timeout=60000)
→ if still running: heartbeat messages visible
→ if done: full output with inner command results + status line

Repeat polling until you see === Playground: SUCCESS === or === Playground: FAILED ===.

Step 3: Interpret the results. See "Interpreting results" below.

Examples

Simple command:

with-playground.sh "dagger version"

Working with source code (mounted at ./src):

with-playground.sh "cd src/dagger && dagger functions"

Multi-line scripts and heredocs work reliably:

with-playground.sh '
mkdir -p /tmp/test/.dagger && cd /tmp/test
cat > .dagger/config.toml <<TOML
[modules.wolfi]
source = "github.com/dagger/dagger/modules/wolfi"
TOML
dagger functions
'

The script writes the inner command to a file inside the container, then executes it. This avoids quoting issues with special characters, newlines, and nested heredocs. The script builds the playground, mounts sample source code at ./src, executes the command, and prints combined output.

Environment variables

You may set these environment variables to customize execution of with-playground.sh

Interpreting results

The script manages output formatting, error extraction, and status reporting. See comments in with-playground.sh for implementation details. Here's what to look for in the output:

• Still running (polling): Heartbeat messages but no status line → poll again.
• Success: Look for === Playground: SUCCESS === at the end. Inner command output appears above it.
• Engine crash: Look for panic: with a goroutine stack trace. The script extracts panics automatically, even if they occurred early in the build. Trace backward from the panic to find root cause (often a nil field on a partially-initialized struct).
• Empty inner command output: The dagger pipeline failed before reaching your inner command. Check the progress trace below it for the error.
• Silent failure: Exit code non-zero with no panic. A progress trace section with error details appears after the inner command output.
• Timeout (exit code 124): The inner command hung (deadlock, infinite loop). Look for === TIMEOUT === at the end. Reduce scope of the inner command to isolate the hang.

Remember, dagger logs not just the execution of your inner command, but the entire process of building a complete dagger engine, dagger CLI, and the execution environment wrapping them; then running the dev engine as a service (including streaming its logs) while concurrently executing your inner command. Keep this in mind when reading logs.

Integration Tests

FIXME