diff --git a/parso/pgen2/grammar_parser.py b/parso/pgen2/grammar_parser.py
index 623a455..0be7209 100644
--- a/parso/pgen2/grammar_parser.py
+++ b/parso/pgen2/grammar_parser.py
@@ -141,6 +141,9 @@ class NFAArc(object):
         self.next = next_
         self.nonterminal_or_string = nonterminal_or_string
 
+    def __repr__(self):
+        return '<%s: %s>' % (self.__class__.__name__, self.nonterminal_or_string)
+
 
 class NFAState(object):
     def __init__(self, from_rule):
diff --git a/test/test_pgen2.py b/test/test_pgen2.py
index 6ec081b..30b0c23 100644
--- a/test/test_pgen2.py
+++ b/test/test_pgen2.py
@@ -292,41 +292,22 @@ def test_left_recursion():
         generate_grammar('foo: foo NAME\n', tokenize.PythonTokenTypes)
 
 
-def test_ambiguities():
-    with pytest.raises(
-        ValueError,
-        match=r"foo is ambiguous.*given a TokenType\(NAME\).*bar or baz"
-    ):
-        generate_grammar('foo: bar | baz\nbar: NAME\nbaz: NAME\n', tokenize.PythonTokenTypes)
-
-    with pytest.raises(
-        ValueError,
-        match=r"foo is ambiguous.*given a ReservedString\(x\).*bar or baz"
-    ):
-        generate_grammar('''foo: bar | baz\nbar: 'x'\nbaz: "x"\n''', tokenize.PythonTokenTypes)
-
-    with pytest.raises(
-        ValueError,
-        match=r"foo is ambiguous.*given a ReservedString\(x\).*bar or foo"
-    ):
-        generate_grammar('''foo: bar | 'x'\nbar: 'x'\n''', tokenize.PythonTokenTypes)
-
-    # an ambiguity with the second (not the first) child of a production
-    with pytest.raises(
-        ValueError,
-        match=r"outer is ambiguous.*given a ReservedString\(b\).*inner or outer"
-    ):
-        generate_grammar(
-            'outer: "a" [inner] "b" "c"\ninner: "b" "c" [inner]\n',
-            tokenize.PythonTokenTypes,
-        )
-
-    # an ambiguity hidden by a level of indirection (middle)
-    with pytest.raises(
-        ValueError,
-        match=r"outer is ambiguous.*given a ReservedString\(b\).*middle or outer"
-    ):
-        generate_grammar(
-            'outer: "a" [middle] "b" "c"\nmiddle: inner\ninner: "b" "c" [inner]\n',
-            tokenize.PythonTokenTypes,
-        )
+@pytest.mark.parametrize(
+    'grammar, error_match', [
+        ['foo: bar | baz\nbar: NAME\nbaz: NAME\n',
+         r"foo is ambiguous.*given a TokenType\(NAME\).*bar or baz"],
+        ['''foo: bar | baz\nbar: 'x'\nbaz: "x"\n''',
+         r"foo is ambiguous.*given a ReservedString\(x\).*bar or baz"],
+        ['''foo: bar | 'x'\nbar: 'x'\n''',
+         r"foo is ambiguous.*given a ReservedString\(x\).*bar or foo"],
+        # An ambiguity with the second (not the first) child of a production
+        ['outer: "a" [inner] "b" "c"\ninner: "b" "c" [inner]\n',
+         r"outer is ambiguous.*given a ReservedString\(b\).*inner or outer"],
+        # An ambiguity hidden by a level of indirection (middle)
+        ['outer: "a" [middle] "b" "c"\nmiddle: inner\ninner: "b" "c" [inner]\n',
+         r"outer is ambiguous.*given a ReservedString\(b\).*middle or outer"],
+    ]
+)
+def test_ambiguities(grammar, error_match):
+    with pytest.raises(ValueError, match=error_match):
+        generate_grammar(grammar, tokenize.PythonTokenTypes)