[esnunes]

Fixes the "Test on macOS" failure on #16, which comes from the runner, not from #16's README change.

The failure

On one tuist-macos-26-3 runner, xcodebuild -showdestinations listed only the placeholder for iOS simulators, so the test found no iPhone:

{ platform:iOS Simulator, id:dvtdevice-DVTiOSDeviceSimulatorPlaceholder-iphonesimulator:placeholder, name:Any iOS Simulator Device }

That placeholder appears without an error, which means the iOS simulator runtime is installed. There were just no simulators created on that machine. #18 passed on another runner of the same profile that did have them, so the images apparently differ in whether simulators are pre-created.

The fix

When Xcode lists no iPhone, the test now creates one: simctl create "TestCoverageAttribution iPhone" on the newest iOS runtime from simctl list runtimes available --json, with the first iPhone model that runtime supports. It then asks Xcode again, so it still only uses a device the selected Xcode can run. If even that fails, the message includes Xcode's destination list, as it did before, since that list is what diagnosed this failure.

execute now returns the process's standard output, kept separate from standard error so simctl's JSON parses cleanly. Its callers no longer manage temporary log files, which also covers the cleanup the review of #15 noted.

Verification

• Creation path. In a copy that skips the first lookup and only accepts the created device, the helper created the simulator, Xcode listed it, and all three runners of attributesEachTestToTheCountersItMoved passed on it. I deleted that simulator afterwards.
• Locally. mise run test (8 tests) and mise run lint pass.

Once this merges, #16 needs a rebase to pick it up.

Code review

Fixed:

• Destination list in the failure message. The final message had dropped Xcode's destination list. It's back, which I checked by forcing the failure.

Not changed:

• Newest runtime. The device is created on the newest runtime, even if the selected Xcode can't run it. This doesn't reproduce here: Xcode 26.3 also runs devices on the newer 26.5 runtime. If it ever happens, the failure message shows it.
• Leftover simulators. Created simulators accumulate when Xcode doesn't list them, which only follows from the case above.
• CI coverage. CI only exercises the creation path on runners without simulators.
• Separate output streams. Standard output and standard error are now separate in failure messages instead of interleaved.

🤖 Generated with Claude Code