diff --git a/builders/server/tests/conftest.py b/builders/server/tests/conftest.py
index 3f8b61d..e69de29 100644
--- a/builders/server/tests/conftest.py
+++ b/builders/server/tests/conftest.py
@@ -1,46 +0,0 @@
-from collections.abc import Callable
-from pathlib import Path
-
-import pytest
-
-
-@pytest.fixture
-def mock_scripts_dir(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
-    """Create a temp scripts dir and monkeypatch SCRIPTS_DIR."""
-    scripts = tmp_path / "scripts"
-    scripts.mkdir()
-    from core.runtime import config, loader
-
-    monkeypatch.setattr(config, "SCRIPTS_DIR", scripts)
-    monkeypatch.setattr(loader, "SCRIPTS_DIR", scripts)
-    return scripts
-
-
-@pytest.fixture
-def write_config(tmp_path: Path) -> Callable[[Path, str, str, str], Path]:
-    """Factory fixture to write config.toml files under the scripts dir."""
-
-    def _write(
-        scripts_dir: Path, dataset_name: str, dataset_version: str, content: str
-    ) -> Path:
-        d = scripts_dir / dataset_name / dataset_version
-        d.mkdir(parents=True, exist_ok=True)
-        (d / "config.toml").write_text(content)
-        return d
-
-    return _write
-
-
-@pytest.fixture
-def write_builder(tmp_path: Path) -> Callable[[Path, str, str, str], Path]:
-    """Factory fixture to write builder.py files under the scripts dir."""
-
-    def _write(
-        scripts_dir: Path, dataset_name: str, dataset_version: str, content: str
-    ) -> Path:
-        d = scripts_dir / dataset_name / dataset_version
-        d.mkdir(parents=True, exist_ok=True)
-        (d / "builder.py").write_text(content)
-        return d
-
-    return _write
diff --git a/builders/server/tests/api/__init__.py b/builders/server/tests/core/__init__.py
similarity index 100%
rename from builders/server/tests/api/__init__.py
rename to builders/server/tests/core/__init__.py
diff --git a/builders/server/tests/calendars/__init__.py b/builders/server/tests/core/api/__init__.py
similarity index 100%
rename from builders/server/tests/calendars/__init__.py
rename to builders/server/tests/core/api/__init__.py
diff --git a/builders/server/tests/api/test_routes.py b/builders/server/tests/core/api/test_routes.py
similarity index 100%
rename from builders/server/tests/api/test_routes.py
rename to builders/server/tests/core/api/test_routes.py
diff --git a/builders/server/tests/calendars/definitions/__init__.py b/builders/server/tests/core/calendars/__init__.py
similarity index 100%
rename from builders/server/tests/calendars/definitions/__init__.py
rename to builders/server/tests/core/calendars/__init__.py
diff --git a/builders/server/tests/db/__init__.py b/builders/server/tests/core/calendars/definitions/__init__.py
similarity index 100%
rename from builders/server/tests/db/__init__.py
rename to builders/server/tests/core/calendars/definitions/__init__.py
diff --git a/builders/server/tests/calendars/definitions/test_always_open.py b/builders/server/tests/core/calendars/definitions/test_always_open.py
similarity index 100%
rename from builders/server/tests/calendars/definitions/test_always_open.py
rename to builders/server/tests/core/calendars/definitions/test_always_open.py
diff --git a/builders/server/tests/calendars/definitions/test_everyday.py b/builders/server/tests/core/calendars/definitions/test_everyday.py
similarity index 100%
rename from builders/server/tests/calendars/definitions/test_everyday.py
rename to builders/server/tests/core/calendars/definitions/test_everyday.py
diff --git a/builders/server/tests/calendars/definitions/test_nyse_daily.py b/builders/server/tests/core/calendars/definitions/test_nyse_daily.py
similarity index 100%
rename from builders/server/tests/calendars/definitions/test_nyse_daily.py
rename to builders/server/tests/core/calendars/definitions/test_nyse_daily.py
diff --git a/builders/server/tests/calendars/definitions/test_weekday.py b/builders/server/tests/core/calendars/definitions/test_weekday.py
similarity index 100%
rename from builders/server/tests/calendars/definitions/test_weekday.py
rename to builders/server/tests/core/calendars/definitions/test_weekday.py
diff --git a/builders/server/tests/calendars/test_utils.py b/builders/server/tests/core/calendars/test_utils.py
similarity index 100%
rename from builders/server/tests/calendars/test_utils.py
rename to builders/server/tests/core/calendars/test_utils.py
diff --git a/builders/server/tests/core/conftest.py b/builders/server/tests/core/conftest.py
new file mode 100644
index 0000000..3f8b61d
--- /dev/null
+++ b/builders/server/tests/core/conftest.py
@@ -0,0 +1,46 @@
+from collections.abc import Callable
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture
+def mock_scripts_dir(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
+    """Create a temp scripts dir and monkeypatch SCRIPTS_DIR."""
+    scripts = tmp_path / "scripts"
+    scripts.mkdir()
+    from core.runtime import config, loader
+
+    monkeypatch.setattr(config, "SCRIPTS_DIR", scripts)
+    monkeypatch.setattr(loader, "SCRIPTS_DIR", scripts)
+    return scripts
+
+
+@pytest.fixture
+def write_config(tmp_path: Path) -> Callable[[Path, str, str, str], Path]:
+    """Factory fixture to write config.toml files under the scripts dir."""
+
+    def _write(
+        scripts_dir: Path, dataset_name: str, dataset_version: str, content: str
+    ) -> Path:
+        d = scripts_dir / dataset_name / dataset_version
+        d.mkdir(parents=True, exist_ok=True)
+        (d / "config.toml").write_text(content)
+        return d
+
+    return _write
+
+
+@pytest.fixture
+def write_builder(tmp_path: Path) -> Callable[[Path, str, str, str], Path]:
+    """Factory fixture to write builder.py files under the scripts dir."""
+
+    def _write(
+        scripts_dir: Path, dataset_name: str, dataset_version: str, content: str
+    ) -> Path:
+        d = scripts_dir / dataset_name / dataset_version
+        d.mkdir(parents=True, exist_ok=True)
+        (d / "builder.py").write_text(content)
+        return d
+
+    return _write
diff --git a/builders/server/tests/runtime/__init__.py b/builders/server/tests/core/db/__init__.py
similarity index 100%
rename from builders/server/tests/runtime/__init__.py
rename to builders/server/tests/core/db/__init__.py
diff --git a/builders/server/tests/db/test_connection.py b/builders/server/tests/core/db/test_connection.py
similarity index 100%
rename from builders/server/tests/db/test_connection.py
rename to builders/server/tests/core/db/test_connection.py
diff --git a/builders/server/tests/db/test_datasets.py b/builders/server/tests/core/db/test_datasets.py
similarity index 100%
rename from builders/server/tests/db/test_datasets.py
rename to builders/server/tests/core/db/test_datasets.py
diff --git a/builders/server/tests/service/__init__.py b/builders/server/tests/core/runtime/__init__.py
similarity index 100%
rename from builders/server/tests/service/__init__.py
rename to builders/server/tests/core/runtime/__init__.py
diff --git a/builders/server/tests/runtime/test_config.py b/builders/server/tests/core/runtime/test_config.py
similarity index 100%
rename from builders/server/tests/runtime/test_config.py
rename to builders/server/tests/core/runtime/test_config.py
diff --git a/builders/server/tests/runtime/test_loader.py b/builders/server/tests/core/runtime/test_loader.py
similarity index 100%
rename from builders/server/tests/runtime/test_loader.py
rename to builders/server/tests/core/runtime/test_loader.py
diff --git a/builders/server/tests/runtime/test_registry.py b/builders/server/tests/core/runtime/test_registry.py
similarity index 100%
rename from builders/server/tests/runtime/test_registry.py
rename to builders/server/tests/core/runtime/test_registry.py
diff --git a/builders/server/tests/runtime/test_runner.py b/builders/server/tests/core/runtime/test_runner.py
similarity index 100%
rename from builders/server/tests/runtime/test_runner.py
rename to builders/server/tests/core/runtime/test_runner.py
diff --git a/builders/server/tests/runtime/test_serialization.py b/builders/server/tests/core/runtime/test_serialization.py
similarity index 100%
rename from builders/server/tests/runtime/test_serialization.py
rename to builders/server/tests/core/runtime/test_serialization.py
diff --git a/builders/server/tests/runtime/test_validator.py b/builders/server/tests/core/runtime/test_validator.py
similarity index 100%
rename from builders/server/tests/runtime/test_validator.py
rename to builders/server/tests/core/runtime/test_validator.py
diff --git a/builders/server/tests/runtime/test_venv_management.py b/builders/server/tests/core/runtime/test_venv_management.py
similarity index 100%
rename from builders/server/tests/runtime/test_venv_management.py
rename to builders/server/tests/core/runtime/test_venv_management.py
diff --git a/builders/server/tests/utils/__init__.py b/builders/server/tests/core/service/__init__.py
similarity index 100%
rename from builders/server/tests/utils/__init__.py
rename to builders/server/tests/core/service/__init__.py
diff --git a/builders/server/tests/service/conftest.py b/builders/server/tests/core/service/conftest.py
similarity index 100%
rename from builders/server/tests/service/conftest.py
rename to builders/server/tests/core/service/conftest.py
diff --git a/builders/server/tests/service/test_builder.py b/builders/server/tests/core/service/test_builder.py
similarity index 100%
rename from builders/server/tests/service/test_builder.py
rename to builders/server/tests/core/service/test_builder.py
diff --git a/builders/server/tests/service/test_catalog.py b/builders/server/tests/core/service/test_catalog.py
similarity index 100%
rename from builders/server/tests/service/test_catalog.py
rename to builders/server/tests/core/service/test_catalog.py
diff --git a/builders/server/tests/service/test_concurrent_builds.py b/builders/server/tests/core/service/test_concurrent_builds.py
similarity index 100%
rename from builders/server/tests/service/test_concurrent_builds.py
rename to builders/server/tests/core/service/test_concurrent_builds.py
diff --git a/builders/server/tests/service/test_locks.py b/builders/server/tests/core/service/test_locks.py
similarity index 100%
rename from builders/server/tests/service/test_locks.py
rename to builders/server/tests/core/service/test_locks.py
diff --git a/builders/server/tests/service/test_models.py b/builders/server/tests/core/service/test_models.py
similarity index 100%
rename from builders/server/tests/service/test_models.py
rename to builders/server/tests/core/service/test_models.py
diff --git a/builders/server/tests/service/test_orchestrator.py b/builders/server/tests/core/service/test_orchestrator.py
similarity index 100%
rename from builders/server/tests/service/test_orchestrator.py
rename to builders/server/tests/core/service/test_orchestrator.py
diff --git a/builders/server/tests/service/test_scheduler.py b/builders/server/tests/core/service/test_scheduler.py
similarity index 100%
rename from builders/server/tests/service/test_scheduler.py
rename to builders/server/tests/core/service/test_scheduler.py
diff --git a/builders/server/tests/service/test_worker.py b/builders/server/tests/core/service/test_worker.py
similarity index 100%
rename from builders/server/tests/service/test_worker.py
rename to builders/server/tests/core/service/test_worker.py
diff --git a/builders/server/tests/core/utils/__init__.py b/builders/server/tests/core/utils/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/builders/server/tests/utils/test_retry.py b/builders/server/tests/core/utils/test_retry.py
similarity index 100%
rename from builders/server/tests/utils/test_retry.py
rename to builders/server/tests/core/utils/test_retry.py
diff --git a/builders/server/tests/utils/test_semver.py b/builders/server/tests/core/utils/test_semver.py
similarity index 100%
rename from builders/server/tests/utils/test_semver.py
rename to builders/server/tests/core/utils/test_semver.py