diff --git a/test/unit_tests/coordinate_transformer_test.py b/test/unit_tests/coordinate_transformer_test.py
index 0e4201c..cb62da3 100644
--- a/test/unit_tests/coordinate_transformer_test.py
+++ b/test/unit_tests/coordinate_transformer_test.py
@@ -115,6 +115,9 @@ def coordinate_test_page_image(coordinate_test_pdf):
 @pytest.mark.parametrize("corner", ["top_left", "bottom_left"])
 @pytest.mark.parametrize("coordinate_system", ["fpdf"])
 def test_fpdf_coordinate_transformer(position_metadata_in_given_system, position_metadata_in_reference_system):
+    """We use FPDF's coordinate system as the reference system (arbitrarily). Hence, FPDFCoordinateTransformer
+    actually does not do anything. This test merely documents the fact, that FPDF is the reference system.
+    """
     transformer = FPDFCoordinateTransformer()
     assert transformer.forward(position_metadata_in_given_system) == position_metadata_in_reference_system
     assert transformer.backward(position_metadata_in_reference_system) == position_metadata_in_given_system
@@ -128,6 +131,12 @@ def test_fpdf_coordinate_transformer(position_metadata_in_given_system, position
 @pytest.mark.parametrize("corner", ["top_left", "bottom_left"])
 @pytest.mark.parametrize("coordinate_system", ["fitz"])
 def test_fitz_coordinate_transformer(position_metadata_in_given_system, position_metadata_in_reference_system):
+    """How I inferred the transformation:
+
+    - extract images from coordinate_test_fpdf with ParsablePDFImageExtractor (see test_parsable_pdf_image_extractor)
+    - Compare position_metadata_in_given_system (fitz) with position_metadata_in_reference_system (fpdf)
+    - Observe that they are identical
+    """
     transformer = FitzCoordinateTransformer()
     assert transformer.forward(position_metadata_in_given_system) == position_metadata_in_reference_system
     assert transformer.backward(position_metadata_in_reference_system) == position_metadata_in_given_system
@@ -141,6 +150,13 @@ def test_fitz_coordinate_transformer(position_metadata_in_given_system, position
 @pytest.mark.parametrize("corner", ["top_left", "bottom_left"])
 @pytest.mark.parametrize("coordinate_system", ["pdfnet"])
 def test_pdfnet_coordinate_transformer(position_metadata_in_given_system, position_metadata_in_reference_system):
+    """How I inferred the transformation:
+
+    - save coordinate_test_fpdf to disk as file f
+    - draw boxes for position_metadata_in_reference_system in f with draw_metadata_box
+    - save annotated pdf as file g
+    - look at discrepancy between the black square and the red box in g
+    """
     transformer = PDFNetCoordinateTransformer()
 
     assert transformer.forward(position_metadata_in_reference_system) == position_metadata_in_given_system