Add tests.

tests/test_compat.py

@@ -0,0 +1,17 @@
+"""
+test that function in compati behave the same
+
+"""
+
+import pytest
+
+from micropip._compat import HttpStatusError, fetch_string_and_headers
+
+
+@pytest.mark.asyncio
+async def test_404_raise(httpserver):
+    httpserver.expect_request("/404").respond_with_data(
+        "Not found", status=404, content_type="text/plain"
+    )
+    with pytest.raises(HttpStatusError):
+        await fetch_string_and_headers(httpserver.url_for("/404"), {})