add test_load_test_credentials

tests/test_coordinator.py

@@ -0,0 +1,18 @@
+import os
+from pathlib import Path
+
+from pytest_abra.coordinator import Coordinator
+from pytest_abra.dir_manager import DirManager
+
+
+def test_load_test_credentials(tmp_path: Path):
+    assert "TEST_USER" not in os.environ
+
+    DIR = DirManager(output_dir=tmp_path, session_id="abc")
+    DIR.create_all_dirs()
+
+    Coordinator.load_test_credentials(DIR)
+
+    assert "TEST_USER" in os.environ
+
+    assert (DIR.STATES / "credentials_test.json").is_file()