Move unit tests to their own sub-dir in tests

tests/unit_tests/utilities/__init__.py

@@ -0,0 +1,26 @@
+"""Utilities for testing and debugging.
+
+At the top level are some basic testing functions. More specific testing utilities are
+provided by modules inside the package.
+"""
+
+from collections.abc import Hashable
+from typing import Iterable, Protocol
+
+
+class SizedIterableHashable(Iterable[Hashable], Protocol):
+    """A protocol for sized iterable of hashable objects."""
+
+    def __len__(self) -> int:
+        """Add a len function to protocol so Python knows the object is sized."""
+
+
+def assert_unique_of_length(data: SizedIterableHashable, length: int) -> None:
+    """Assert that a list (or other iterable) has unique contents of a given length.
+
+    :param data: A list or other sized iterable of hashable objects. To be checked
+    for unique contents and length.
+    :param length: The expected length of data
+    """
+    assert len(data) == len(set(data))
+    assert len(data) == length