create the _pytest/assertion package

_pytest/assertion/__init__.py

@@ -9,7 +9,7 @@ import sys
 from _pytest.monkeypatch import monkeypatch
 
 try:
-    from _pytest.assertrewrite import rewrite_asserts
+    from _pytest.assertion.rewrite import rewrite_asserts
 except ImportError:
     rewrite_asserts = None
 else:

_pytest/assertion/rewrite.py

@@ -95,7 +95,7 @@ class AssertionRewriter(ast.NodeVisitor):
         # docstrings and __future__ imports.
         aliases = [ast.alias(py.builtin.builtins.__name__, "@py_builtins"),
                    ast.alias("py", "@pylib"),
-                   ast.alias("_pytest.assertrewrite", "@pytest_ar")]
+                   ast.alias("_pytest.assertion.rewrite", "@pytest_ar")]
         expect_docstring = True
         pos = 0
         lineno = 0

testing/test_assertrewrite.py

@@ -4,7 +4,7 @@ import pytest
 
 ast = pytest.importorskip("ast")
 
-from _pytest.assertrewrite import rewrite_asserts
+from _pytest.assertion.rewrite import rewrite_asserts
 
 
 def setup_module(mod):