diff --git a/tests/backend/tiles/test_utils.py b/tests/backend/tiles/test_utils.py
new file mode 100644
index 0000000000..bbef233ca5
--- /dev/null
+++ b/tests/backend/tiles/test_utils.py
@@ -0,0 +1,101 @@
+import numpy as np
+import pytest
+
+from invokeai.backend.tiles.utils import TBLR, paste
+
+
+def test_paste_no_mask_success():
+    """Test successful paste with mask=None."""
+    dst_image = np.zeros((5, 5, 3), dtype=np.uint8)
+
+    # Create src_image with a pattern that can be used to validate that it was pasted correctly.
+    src_image = np.zeros((3, 3, 3), dtype=np.uint8)
+    src_image[0, :, 0] = 1  # Row of 1s in channel 0.
+    src_image[:, 0, 1] = 2  # Column of 2s in channel 1.
+
+    # Paste in bottom-center of dst_image.
+    box = TBLR(top=2, bottom=5, left=1, right=4)
+
+    # Construct expected output image.
+    expected_output = np.zeros((5, 5, 3), dtype=np.uint8)
+    expected_output[2, 1:4, 0] = 1
+    expected_output[2:5, 1, 1] = 2
+
+    paste(dst_image=dst_image, src_image=src_image, box=box)
+
+    np.testing.assert_array_equal(dst_image, expected_output, strict=True)
+
+
+def test_paste_with_mask_success():
+    """Test successful paste with a mask."""
+    dst_image = np.zeros((5, 5, 3), dtype=np.uint8)
+
+    # Create src_image with a pattern that can be used to validate that it was pasted correctly.
+    src_image = np.zeros((3, 3, 3), dtype=np.uint8)
+    src_image[0, :, 0] = 64  # Row of 64s in channel 0.
+    src_image[:, 0, 1] = 128  # Column of 128s in channel 1.
+
+    # Paste in bottom-center of dst_image.
+    box = TBLR(top=2, bottom=5, left=1, right=4)
+
+    # Create a mask that blends the top-left corner of 'src_image' at 50%, and ignores the rest of src_image.
+    mask = np.zeros((3, 3))
+    mask[0, 0] = 0.5
+
+    # Construct expected output image.
+    expected_output = np.zeros((5, 5, 3), dtype=np.uint8)
+    expected_output[2, 1, 0] = 32
+    expected_output[2, 1, 1] = 64
+
+    paste(dst_image=dst_image, src_image=src_image, box=box, mask=mask)
+
+    np.testing.assert_array_equal(dst_image, expected_output, strict=True)
+
+
+@pytest.mark.parametrize("use_mask", [True, False])
+def test_paste_box_overflows_dst_image(use_mask: bool):
+    """Test that an exception is raised if 'box' overflows the 'dst_image'."""
+    dst_image = np.zeros((5, 5, 3), dtype=np.uint8)
+    src_image = np.zeros((3, 3, 3), dtype=np.uint8)
+    mask = None
+    if use_mask:
+        mask = np.zeros((3, 3))
+
+    # Construct box that overflows bottom of dst_image.
+    top = 3
+    left = 0
+    box = TBLR(top=top, bottom=top + src_image.shape[0], left=left, right=left + src_image.shape[1])
+
+    with pytest.raises(ValueError):
+        paste(dst_image=dst_image, src_image=src_image, box=box, mask=mask)
+
+
+@pytest.mark.parametrize("use_mask", [True, False])
+def test_paste_src_image_does_not_match_box(use_mask: bool):
+    """Test that an exception is raised if the 'src_image' shape does not match the 'box' dimensions."""
+    dst_image = np.zeros((5, 5, 3), dtype=np.uint8)
+    src_image = np.zeros((3, 3, 3), dtype=np.uint8)
+    mask = None
+    if use_mask:
+        mask = np.zeros((3, 3))
+
+    # Construct box that is smaller than src_image.
+    box = TBLR(top=0, bottom=src_image.shape[0] - 1, left=0, right=src_image.shape[1])
+
+    with pytest.raises(ValueError):
+        paste(dst_image=dst_image, src_image=src_image, box=box, mask=mask)
+
+
+def test_paste_mask_does_not_match_src_image():
+    """Test that an exception is raised if the 'mask' shape is different than the 'src_image' shape."""
+    dst_image = np.zeros((5, 5, 3), dtype=np.uint8)
+    src_image = np.zeros((3, 3, 3), dtype=np.uint8)
+
+    # Construct mask that is smaller than the src_image.
+    mask = np.zeros((src_image.shape[0] - 1, src_image.shape[1]))
+
+    # Construct box that matches src_image shape.
+    box = TBLR(top=0, bottom=src_image.shape[0], left=0, right=src_image.shape[1])
+
+    with pytest.raises(ValueError):
+        paste(dst_image=dst_image, src_image=src_image, box=box, mask=mask)