place assertion imports after __future__ statements and docstrings

_pytest/assertrewrite.py

@@ -74,15 +74,23 @@ class AssertionRewriter(ast.NodeVisitor):
         if not mod.body:
             # Nothing to do.
             return
-        # Insert some special imports at top but after any docstrings.
+        # Insert some special imports at top but after any docstrings and
+        # __future__ imports.
         aliases = [ast.alias(py.builtin.builtins.__name__, "@py_builtins"),
                    ast.alias("py", "@pylib"),
                    ast.alias("_pytest.assertrewrite", "@pytest_ar")]
         imports = [ast.Import([alias], lineno=0, col_offset=0)
                    for alias in aliases]
+        expect_docstring = True
         pos = 0
-        if isinstance(mod.body[0], ast.Str):
+        for item in mod.body:
-            pos = 1
+            if (expect_docstring and isinstance(item, ast.Expr) and
+                isinstance(item.value, ast.Str)):
+                expect_docstring = False
+            elif (not isinstance(item, ast.ImportFrom) or item.level > 0 and
+                  item.identifier != "__future__"):
+                break
+            pos += 1
         mod.body[pos:pos] = imports
         # Collect asserts.
         asserts = []

testing/test_assertrewrite.py

@@ -16,11 +16,15 @@ def teardown_module(mod):
     del mod._old_reprcompare
 
 
+def rewrite(src):
+    tree = ast.parse(src)
+    rewrite_asserts(tree)
+    return tree
+
 def getmsg(f, extra_ns=None, must_pass=False):
     """Rewrite the assertions in f, run it, and get the failure message."""
     src = '\n'.join(py.code.Code(f).source().lines)
-    mod = ast.parse(src)
+    mod = rewrite(src)
-    rewrite_asserts(mod)
     code = compile(mod, "<test>", "exec")
     ns = {}
     if extra_ns is not None:
@@ -43,6 +47,26 @@ def getmsg(f, extra_ns=None, must_pass=False):
 
 class TestAssertionRewrite:
 
+    def test_place_initial_imports(self):
+        s = """'Doc string'"""
+        m = rewrite(s)
+        assert isinstance(m.body[0], ast.Expr)
+        assert isinstance(m.body[0].value, ast.Str)
+        for imp in m.body[1:]:
+            assert isinstance(imp, ast.Import)
+        s = """from __future__ import with_statement"""
+        m = rewrite(s)
+        assert isinstance(m.body[0], ast.ImportFrom)
+        for imp in m.body[1:]:
+            assert isinstance(imp, ast.Import)
+        s = """'doc string'\nfrom __future__ import with_statement"""
+        m = rewrite(s)
+        assert isinstance(m.body[0], ast.Expr)
+        assert isinstance(m.body[0].value, ast.Str)
+        assert isinstance(m.body[1], ast.ImportFrom)
+        for imp in m.body[2:]:
+            assert isinstance(imp, ast.Import)
+
     def test_name(self):
         def f():
             assert False