Organize test suite: add README, move loose tests to proper directories

- Add tests/README.md documenting test structure and usage
- Move issue_*_test.py files to tests/regression/ (9 files)
- Move loose test_*.py files to tests/unit/ (18 files)
- tests/ root now contains only pytest infrastructure

Addresses #166

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/regression/issue_190_layer_docs_test.py

@@ -0,0 +1,95 @@
+#!/usr/bin/env python3
+"""Test for issue #190: Expanded TileLayer and ColorLayer __init__ documentation.
+
+This test verifies that the documentation for ColorLayer and TileLayer
+contains the expected key phrases and is comprehensive.
+"""
+import mcrfpy
+import sys
+
+def test_colorlayer_docs():
+    """Test ColorLayer documentation completeness."""
+    doc = mcrfpy.ColorLayer.__doc__
+
+    if not doc:
+        print("FAIL: ColorLayer.__doc__ is empty or None")
+        return False
+
+    print("=== ColorLayer Documentation ===")
+    print(doc)
+    print()
+
+    # Check for key phrases
+    required_phrases = [
+        "grid_size",
+        "z_index",
+        "RGBA",
+        "at(x, y)",
+        "set(x, y",
+        "fill(",
+        "Grid.add_layer",
+        "visible",
+        "Example",
+    ]
+
+    missing = []
+    for phrase in required_phrases:
+        if phrase not in doc:
+            missing.append(phrase)
+
+    if missing:
+        print(f"FAIL: ColorLayer docs missing phrases: {missing}")
+        return False
+
+    print("ColorLayer documentation: PASS")
+    return True
+
+def test_tilelayer_docs():
+    """Test TileLayer documentation completeness."""
+    doc = mcrfpy.TileLayer.__doc__
+
+    if not doc:
+        print("FAIL: TileLayer.__doc__ is empty or None")
+        return False
+
+    print("=== TileLayer Documentation ===")
+    print(doc)
+    print()
+
+    # Check for key phrases
+    required_phrases = [
+        "grid_size",
+        "z_index",
+        "texture",
+        "at(x, y)",
+        "set(x, y",
+        "fill(",
+        "-1",  # Special value for no tile
+        "sprite",
+        "Grid.add_layer",
+        "visible",
+        "Example",
+    ]
+
+    missing = []
+    for phrase in required_phrases:
+        if phrase not in doc:
+            missing.append(phrase)
+
+    if missing:
+        print(f"FAIL: TileLayer docs missing phrases: {missing}")
+        return False
+
+    print("TileLayer documentation: PASS")
+    return True
+
+# Run tests
+colorlayer_ok = test_colorlayer_docs()
+tilelayer_ok = test_tilelayer_docs()
+
+if colorlayer_ok and tilelayer_ok:
+    print("\nAll documentation tests PASSED")
+    sys.exit(0)
+else:
+    print("\nDocumentation tests FAILED")
+    sys.exit(1)