Ensure printable manually-specified param(id=...)

src/_pytest/mark/structures.py

@@ -8,6 +8,7 @@ import attr
 import six
 from six.moves import map
 
+from ..compat import ascii_escaped
 from ..compat import getfslineno
 from ..compat import MappingMixin
 from ..compat import NOTSET
@@ -77,6 +78,7 @@ class ParameterSet(namedtuple("ParameterSet", "values, marks, id")):
                 raise TypeError(
                     "Expected id to be a string, got {}: {!r}".format(type(id_), id_)
                 )
+            id_ = ascii_escaped(id_)
         return cls(values, marks, id_)
 
     @classmethod

testing/python/metafunc.py

@@ -394,6 +394,18 @@ class TestMetafunc(object):
         )
         assert result == ["\\x00-1", "\\x05-2", "\\x00-3", "\\x05-4"]
 
+    def test_idmaker_manual_ids_must_be_printable(self):
+        from _pytest.python import idmaker
+
+        result = idmaker(
+            ("s",),
+            [
+                pytest.param("x00", id="hello \x00"),
+                pytest.param("x05", id="hello \x05"),
+            ],
+        )
+        assert result == ["hello \\x00", "hello \\x05"]
+
     def test_idmaker_enum(self):
         from _pytest.python import idmaker