Improve test coverage from 63.6% to 73.4% and fix test infrastructure (#137)

pyproject.toml

@@ -82,7 +82,7 @@ asyncio_default_fixture_loop_scope = "function"
 timeout = 30
 timeout_method = "signal"
 timeout_func_only = false
-addopts = "-v --tb=short --strict-markers --disable-warnings -n auto --dist worksteal"
+addopts = "-v --tb=short --strict-markers --disable-warnings --durations=10"
 markers = [
     "unit: Unit tests (fast, no I/O)",
     "integration: Integration tests (may use SQLite)",
@@ -115,7 +115,7 @@ exclude_lines = [
     "@abstractmethod",
 ]
 # Fail CI if coverage drops below this threshold
-fail_under = 60
+fail_under = 73
 
 [tool.coverage.html]
 directory = "htmlcov"