Add unit-test to catch changes to required deps (#3662)

This adds a unit test that can catch changes to required dependencies

tests/unit_tests/test_depedencies.py

@@ -0,0 +1,42 @@
+"""A unit test meant to catch accidental introduction of non-optional dependencies."""
+from pathlib import Path
+
+import toml
+
+HERE = Path(__file__).parent
+
+PYPROJECT_TOML = HERE / "../../pyproject.toml"
+
+
+def test_required_dependencies() -> None:
+    """A test that checks if a new non-optional dependency is being introduced.
+
+    If this test is triggered, it means that a contributor is trying to introduce a new
+    required dependency. This should be avoided in most situations.
+    """
+    with open(PYPROJECT_TOML) as f:
+        pyproject = toml.load(f)
+
+    # Get the dependencies from the [tool.poetry.dependencies] section
+    dependencies = pyproject["tool"]["poetry"]["dependencies"]
+
+    required_dependencies = [
+        package_name
+        for package_name, requirements in dependencies.items()
+        if isinstance(requirements, str) or not requirements.get("optional", False)
+    ]
+
+    assert sorted(required_dependencies) == [
+        "PyYAML",
+        "SQLAlchemy",
+        "aiohttp",
+        "async-timeout",
+        "dataclasses-json",
+        "numexpr",
+        "numpy",
+        "openapi-schema-pydantic",
+        "pydantic",
+        "python",
+        "requests",
+        "tenacity",
+    ]