Increase test coverage for svg.py (#620)

Co-authored-by: Lucas Cimon <925560+Lucas-C@users.noreply.github.com>

test/svg/test_transform_viewport.py

@@ -0,0 +1,43 @@
+import fpdf
+import pytest
+
+
+def test_rect_transform_width_exception():
+    svg_data = """<?xml version="1.0" standalone="no"?>
+    <svg width="10%" height="10cm" viewBox="0 0 1000 1000" xmlns="http://www.w3.org/2000/svg" version="1.1">
+    </svg>
+    """
+
+    svg = fpdf.svg.SVGObject(svg_data)
+    with pytest.raises(ValueError) as error:
+        svg.transform_to_rect_viewport(scale=1, width=None, height=10)
+    assert 'SVG "width" is a percentage, hence a viewport width is required' == str(
+        error.value
+    )
+
+
+def test_rect_transform_height_exception():
+    svg_data = """<?xml version="1.0" standalone="no"?>
+    <svg width="10cm" height="10%" viewBox="0 0 1000 1000" xmlns="http://www.w3.org/2000/svg" version="1.1">
+    </svg>
+    """
+
+    svg = fpdf.svg.SVGObject(svg_data)
+    with pytest.raises(ValueError) as error:
+        svg.transform_to_rect_viewport(scale=1, width=10, height=None)
+    assert 'SVG "height" is a percentage, hence a viewport height is required' == str(
+        error.value
+    )
+
+
+def test_rect_transform_vw_zero():
+    svg_data = """<?xml version="1.0" standalone="no"?>
+    <svg width="10cm" height="10cm" viewBox="0 0 0 1000" xmlns="http://www.w3.org/2000/svg" version="1.1">
+    </svg>
+    """
+
+    svg = fpdf.svg.SVGObject(svg_data)
+    width, height, context = svg.transform_to_rect_viewport(scale=2, width=10, height=5)
+    assert width == 0
+    assert height == 0
+    assert context is not None