Fix ExcellonFile.to_gerber and add a unit test

src/gerbonara/excellon.py

@@ -30,9 +30,10 @@ from pathlib import Path
 
 from .cam import CamFile, FileSettings
 from .graphic_objects import Flash, Line, Arc
-from .apertures import ExcellonTool
+from .apertures import ExcellonTool, CircleAperture
 from .utils import Inch, MM, to_unit, InterpMode, RegexMatcher
 
+
 class ExcellonContext:
     """ Internal helper class used for tracking graphics state when writing Excellon. """
 
@@ -268,17 +269,19 @@ class ExcellonFile(CamFile):
         """ Counterpart to :py:meth:`~.rs274x.GerberFile.to_excellon`. Does nothing and returns :py:obj:`self`. """
         return self
 
-    def to_gerber(self, errros='raise'):
+    def to_gerber(self, errors='raise'):
         """ Convert this excellon file into a :py:class:`~.rs274x.GerberFile`. """
+        from .rs274x import GerberFile
         out = GerberFile()
         out.comments = self.comments
 
         apertures = {}
         for obj in self.objects:
-            if not (ap := apertures[obj.tool]):
-                ap = apertures[obj.tool] = CircleAperture(obj.tool.diameter)
+            if not (ap := apertures.get(obj.tool)):
+                ap = apertures[obj.tool] = CircleAperture(obj.tool.diameter, unit=obj.aperture.unit)
 
             out.objects.append(dataclasses.replace(obj, aperture=ap))
+        return out
 
     @property
     def generator(self):

tests/test_excellon.py

@@ -100,6 +100,28 @@ def test_first_level_idempotence_svg(reference, tmpfile, img_support):
     assert hist[9] == 0
     assert hist[3:].sum() < 5e-5*hist.size
 
+
+@filter_syntax_warnings
+@pytest.mark.parametrize('reference', list(REFERENCE_FILES.items()), indirect=True)
+def test_gerber_conversion(reference, tmpfile, img_support):
+    reference, (unit_spec, _) = reference
+    tmp = tmpfile('Output gerber', '.gbr')
+    ref_svg = tmpfile('Reference SVG render', '.svg')
+    out_svg = tmpfile('Output SVG render', '.svg')
+
+    a = ExcellonFile.open(reference)
+    a.to_gerber().save(tmp)
+    b = GerberFile.open(tmp)
+
+    ref_svg.write_text(str(a.to_svg(fg='black', bg='white')))
+    out_svg.write_text(str(b.to_svg(fg='black', bg='white')))
+
+    mean, _max, hist = img_support.svg_difference(ref_svg, out_svg, diff_out=tmpfile('Difference', '.png'), background='white')
+    assert mean < 2e-4
+    assert hist[9] == 0
+    assert hist[3:].sum() < 2e-4*hist.size
+
+
 @filter_syntax_warnings
 @pytest.mark.parametrize('reference', list(REFERENCE_FILES.items()), indirect=True)
 def test_idempotence(reference, tmpfile):
@@ -123,6 +145,7 @@ def test_idempotence(reference, tmpfile):
 
     assert tmp_1.read_text() == tmp_2.read_text()
 
+
 @filter_syntax_warnings
 @pytest.mark.parametrize('reference', list(REFERENCE_FILES.items()), indirect=True)
 def test_gerber_alignment(reference, tmpfile, print_on_error):