fix: keep negative arc values

Author: nedbat

coverage/jsonreport.py

@@ -115,4 +115,4 @@ def _convert_branch_arcs(branch_arcs):
     """Convert branch arcs to a list of two-element tuples."""
     for source, targets in branch_arcs.items():
         for target in targets:
-            yield source, target if target != -1 else 0
+            yield source, target

tests/test_json.py

@@ -55,7 +55,7 @@ def test_branch_coverage(self):
                     'executed_branches': [
                         [2, 4],
                         [4, 5],
-                        [8, 0],
+                        [8, -1],
                     ],
                     'missing_branches': [
                         [2, 3],