test: migrate to pytest

CONTRIBUTING.md

@@ -31,18 +31,22 @@ uv run ty check drift/ tests/          # Type check
 ### Unit Tests
 
 ```bash
-uv run python -m unittest discover -s tests/unit -v
+uv run pytest tests/unit/ -v
 
 # Run a specific test file
-uv run python -m unittest tests.unit.test_json_schema_helper -v
-uv run python -m unittest tests.unit.test_adapters -v
+uv run pytest tests/unit/test_json_schema_helper.py -v
+uv run pytest tests/unit/test_adapters.py -v
+
+# Run a specific test class or function
+uv run pytest tests/unit/test_metrics.py::TestMetricsCollector -v
+uv run pytest tests/unit/test_metrics.py::TestMetricsCollector::test_record_spans_exported -v
 ```
 
 ### Integration Tests
 
 ```bash
 # Flask/FastAPI integration tests
-timeout 30 uv run python -m unittest discover -s tests/integration -v
+timeout 30 uv run pytest tests/integration/ -v
 ```
 
 ### E2E Tests

pyproject.toml

@@ -51,7 +51,8 @@ dev = [
     "python-jsonpath>=0.10",
     "ruff>=0.8.0",
     "ty>=0.0.1a7",
-    "pytest>=8.0.0",
+    "pytest>=8.0.0,<9.0.0",
+    "pytest-mock>=3.15.0",
 ]
 
 [project.urls]

tests/conftest.py

@@ -0,0 +1,46 @@
+"""Pytest configuration and fixtures for Drift Python SDK tests."""
+
+from __future__ import annotations
+
+import os
+import tempfile
+from collections.abc import Generator
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+import pytest
+
+if TYPE_CHECKING:
+    from drift.core.metrics import MetricsCollector
+    from drift.core.tracing.adapters import InMemorySpanAdapter
+
+
+@pytest.fixture
+def temp_dir() -> Generator[Path, None, None]:
+    """Create a temporary directory for test files."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        yield Path(tmpdir)
+
+
+@pytest.fixture
+def original_cwd() -> Generator[str, None, None]:
+    """Save and restore the current working directory."""
+    cwd = os.getcwd()
+    yield cwd
+    os.chdir(cwd)
+
+
+@pytest.fixture
+def in_memory_adapter() -> InMemorySpanAdapter:
+    """Create a fresh InMemorySpanAdapter for testing."""
+    from drift.core.tracing.adapters import InMemorySpanAdapter
+
+    return InMemorySpanAdapter()
+
+
+@pytest.fixture
+def metrics_collector() -> MetricsCollector:
+    """Create a fresh MetricsCollector for testing."""
+    from drift.core.metrics import MetricsCollector
+
+    return MetricsCollector()