make concurrent

tests/test_development.py

@@ -1,3 +1,4 @@
+import asyncio
 from pathlib import Path
 
 import pytest
@@ -74,6 +75,33 @@ async def test_runs_non_executable_shell_script_from_bind_mount(tmp_path) -> Non
     assert (workspace / "selected").read_text() == "mounted\n"
 
 
+async def test_serializes_concurrent_preparation(tmp_path, monkeypatch) -> None:
+    development = environment(tmp_path, ["shared"])
+    script(development.scripts_dir / "shared", "true")
+    started = asyncio.Event()
+    release = asyncio.Event()
+    active = 0
+    maximum_active = 0
+
+    async def run(*_args) -> None:
+        nonlocal active, maximum_active
+        active += 1
+        maximum_active = max(maximum_active, active)
+        started.set()
+        await release.wait()
+        active -= 1
+
+    monkeypatch.setattr(development, "_run", run)
+    first = asyncio.create_task(development.prepare(tmp_path / "first"))
+    await started.wait()
+    second = asyncio.create_task(development.prepare(tmp_path / "second"))
+    await asyncio.sleep(0)
+    release.set()
+    await asyncio.gather(first, second)
+
+    assert maximum_active == 1
+
+
 async def test_reports_script_failure_output(tmp_path) -> None:
     workspace = tmp_path / "workspace"
     workspace.mkdir()