How to debug Zig tests in VSCode

zig_test_debugging_vscode.md

Tested on macOS:

1. Install the CodeLLDB VSCode extension. Unlike the debugger in the C/C++ extension, this allows to set breakpoints inside Zig "test" blocks (in the MS C/C++ extension debugger, breakpoints inside test blocks will be disabled once the debugger starts for unknown reasons.
2. When compiling the test, tell it to also emit a binary: zig test -femit-bin=zig-out/bin/my-test src/bla.zig, otherwise there will be no executable to debug.
3. The compiled test executable expects the path to the Zig executable as first command line argument, the launch.json file needs to be setup accordingly (note the args item):

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "lldb",
            "request": "launch",
            "name": "Debug",
            "program": "${workspaceFolder}/zig-out/bin/my-test",
            "args": ["/usr/local/bin/zig"],
            "cwd": "${workspaceFolder}",
            
        }
    ]
}

That should be all, now set breakpoints inside tests and start the debugger with F5.

I found that the above solution runs tests twice. I was able to fix this with some slight modifications:

launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "lldb",
            "request": "launch",
            "name": "Debug test",
            "program": "${workspaceFolder}/zig-out/bin/${fileBasenameNoExtension}-test",
            "args": [],
            "cwd": "${workspaceFolder}",
            "preLaunchTask": "test",
        }
    ]
}

tasks.json

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "test",
            "type": "shell",
            "command": "zig",
            "args": [
                "test",
                "-femit-bin=zig-out/bin/${fileBasenameNoExtension}-test",
                "--test-no-exec",
                "${relativeFile}",
            ]
        }
    ]
}

Notice the additional argument --test-no-exec. This will cause the test runner to emit the binary test file without actually running the tests.