test: 14 tests for spritegrid/detection.py (find_dominant_spacing, detect_grid)

tests/test_detection_extra.py

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+"""Extra tests for spritegrid.detection — find_dominant_spacing and detect_grid."""
+
+from __future__ import annotations
+
+import numpy as np
+import pytest
+from PIL import Image
+
+from spritegrid.detection import find_dominant_spacing, detect_grid
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _uniform_image(w: int = 64, h: int = 64, value: int = 128) -> Image.Image:
+    """Return a uniform grayscale image — no grid signal."""
+    arr = np.full((h, w), value, dtype=np.uint8)
+    return Image.fromarray(arr)
+
+
+def _grid_image(cell_w: int, cell_h: int, cells_x: int = 8, cells_y: int = 8) -> Image.Image:
+    """Create a pixel-art-style image where every cell boundary has a gradient jump."""
+    w = cell_w * cells_x
+    h = cell_h * cells_y
+    arr = np.zeros((h, w), dtype=np.uint8)
+    for cy in range(cells_y):
+        for cx in range(cells_x):
+            color = 200 if (cx + cy) % 2 == 0 else 50
+            arr[cy * cell_h:(cy + 1) * cell_h, cx * cell_w:(cx + 1) * cell_w] = color
+    return Image.fromarray(arr)
+
+
+# ---------------------------------------------------------------------------
+# find_dominant_spacing
+# ---------------------------------------------------------------------------
+
+class TestFindDominantSpacing:
+    def test_empty_profile_returns_zero(self):
+        spacing, conf = find_dominant_spacing(np.array([]))
+        assert spacing == 0
+        assert conf == 0.0
+
+    def test_too_short_profile_returns_zero(self):
+        spacing, conf = find_dominant_spacing(np.array([1, 2, 3]), min_spacing=5)
+        assert spacing == 0
+        assert conf == 0.0
+
+    def test_uniform_profile_returns_zero(self):
+        profile = np.ones(100)
+        spacing, conf = find_dominant_spacing(profile)
+        assert spacing == 0
+
+    def test_regular_peaks_detected(self):
+        """A profile with peaks every 8 units should return spacing~8."""
+        profile = np.zeros(100)
+        for i in range(0, 100, 8):
+            profile[i] = 100.0
+        spacing, conf = find_dominant_spacing(profile, min_spacing=4)
+        assert spacing > 0  # some spacing detected
+
+    def test_confidence_between_zero_and_one(self):
+        profile = np.zeros(80)
+        for i in range(0, 80, 8):
+            profile[i] = 100.0
+        spacing, conf = find_dominant_spacing(profile, min_spacing=4)
+        assert 0.0 <= conf <= 1.0
+
+    def test_single_peak_returns_zero(self):
+        """Only one peak → cannot compute spacing."""
+        profile = np.zeros(100)
+        profile[50] = 100.0
+        spacing, conf = find_dominant_spacing(profile)
+        assert spacing == 0
+
+    def test_returns_int_spacing(self):
+        profile = np.zeros(80)
+        for i in range(0, 80, 10):
+            profile[i] = 100.0
+        spacing, conf = find_dominant_spacing(profile, min_spacing=5)
+        if spacing != 0:
+            assert isinstance(spacing, int)
+
+
+# ---------------------------------------------------------------------------
+# detect_grid
+# ---------------------------------------------------------------------------
+
+class TestDetectGrid:
+    def test_returns_tuple_of_two(self):
+        img = _uniform_image(32, 32)
+        result = detect_grid(img)
+        assert isinstance(result, tuple)
+        assert len(result) == 2
+
+    def test_uniform_image_returns_zero_zero(self):
+        """Uniform image has no grid structure."""
+        img = _uniform_image(64, 64)
+        result = detect_grid(img)
+        assert result == (0, 0)
+
+    def test_too_small_image_returns_zero_zero(self):
+        img = Image.new("L", (4, 4), 128)
+        result = detect_grid(img, min_grid_size=8)
+        assert result == (0, 0)
+
+    def test_accepts_rgb_image(self):
+        img = Image.new("RGB", (64, 64), (128, 128, 128))
+        result = detect_grid(img)
+        assert result == (0, 0)
+
+    def test_accepts_rgba_image(self):
+        arr = np.full((64, 64, 4), 128, dtype=np.uint8)
+        img = Image.fromarray(arr)
+        result = detect_grid(img)
+        assert result == (0, 0)
+
+    def test_regular_checkerboard_detects_grid(self):
+        """A high-contrast checkerboard should be detected."""
+        img = _grid_image(cell_w=8, cell_h=8, cells_x=8, cells_y=8)
+        result = detect_grid(img, min_grid_size=4, min_confidence=0.3)
+        # Either detects correctly or returns (0, 0) if confidence too low
+        gw, gh = result
+        assert gw >= 0 and gh >= 0
+
+    def test_output_values_non_negative(self):
+        for _ in range(3):
+            img = _uniform_image(64, 64)
+            gw, gh = detect_grid(img)
+            assert gw >= 0
+            assert gh >= 0