Add test for issue #13

Thanks to @jsfenfen: https://github.com/jsvine/pdfplumber/issues/13

tests/test-issues.py

@@ -12,6 +12,67 @@ HERE = os.path.abspath(os.path.dirname(__file__))
 
 class Test(unittest.TestCase):
 
+    def test_issue_13(self):
+        """
+        Test slightly simplified from gist here: https://github.com/jsvine/pdfplumber/issues/13
+        """
+        pdf = pdfplumber.from_path(
+            os.path.join(HERE, "pdfs/issue-13-151201DSP-Fond-581-90D.pdf")
+        )
+
+        # Only find checkboxes this size
+        RECT_WIDTH = 9.3
+        RECT_HEIGHT = 9.3
+        RECT_TOLERANCE = 2
+
+        def filter_rects(rects):
+            ## Just get the rects that are the right size to be checkboxes
+            rects_found = []
+            for rect in rects:
+                if ( rect['height'] > ( RECT_HEIGHT - RECT_TOLERANCE )   
+                    and ( rect['height'] < RECT_HEIGHT + RECT_TOLERANCE) 
+                    and ( rect['width'] < RECT_WIDTH + RECT_TOLERANCE) 
+                    and ( rect['width'] < RECT_WIDTH + RECT_TOLERANCE) ):
+                    rects_found.append(rect)
+            return rects_found
+
+        def determine_if_checked(checkbox, curve_list):
+            # This figures out if the bounding box of (either) line used to make
+            # one half of the 'x' is the right size and overlaps with a rectangle.
+            # This isn't foolproof, but works for this case. 
+            # It's not totally clear (to me) how common this style of checkboxes
+            # are used, and whether this is useful approach to them.
+            # Also note there should be *two* matching LTCurves for each checkbox.
+            # But here we only test there's at least one. 
+
+            for curve in curve_list:
+
+                if ( checkbox['height'] > ( RECT_HEIGHT - RECT_TOLERANCE )   
+                    and ( checkbox['height'] < RECT_HEIGHT + RECT_TOLERANCE) 
+                    and ( checkbox['width'] < RECT_WIDTH + RECT_TOLERANCE) 
+                    and ( checkbox['width'] < RECT_WIDTH + RECT_TOLERANCE) ):
+
+                    xmatch = False
+                    ymatch = False
+
+                    if ( max(checkbox['x0'], curve['x0']) <= min(checkbox['x1'], curve['x1']) ):
+                        xmatch = True
+                    if ( max(checkbox['y0'], curve['y0']) <= min(checkbox['y1'], curve['y1']) ):
+                        ymatch = True
+                    if xmatch and ymatch:
+                        return True
+
+            return False
+
+        p0 = pdf.pages[0]
+        curves = p0.objects["curve"]
+        rects = filter_rects(p0.objects["rect"])
+
+        n_checked = sum([ determine_if_checked(rect, curves)
+            for rect in rects ])
+
+        assert(n_checked == 5)
+
     def test_issue_14(self):
         pdf = pdfplumber.from_path(
             os.path.join(HERE, "pdfs/cupertino_usd_4-6-16.pdf")