Add test that pins down the order that middleware is executed in

graphql/execution/tests/test_middleware.py

@@ -1,10 +1,12 @@
 # type: ignore
+from __future__ import print_function
+
 import json
 
 from pytest import raises
-
 from graphql.error import GraphQLError
 from graphql.execution import MiddlewareManager, execute
+from graphql.execution.middleware import get_middleware_resolvers, middleware_chain
 from graphql.language.parser import parse
 from graphql.type import (
     GraphQLArgument,
@@ -138,3 +140,52 @@ def resolve(self, next, *args, **kwargs):
         "ok": "ok",
         "not_ok": "not_ok",
     }
+
+
+def test_middleware_chain(capsys):
+    # type: (Any) -> None
+    class CharPrintingMiddleware(object):
+        def __init__(self, char):
+            # type: (str) -> None
+            self.char = char
+
+        def resolve(self, next, *args, **kwargs):
+            # type: (Callable, *Any, **Any) -> str
+            print("resolve() called for middleware {}".format(self.char))
+            return next(*args, **kwargs).then(
+                lambda x: print("then() for {}".format(self.char))
+            )
+
+    middlewares = [
+        CharPrintingMiddleware("a"),
+        CharPrintingMiddleware("b"),
+        CharPrintingMiddleware("c"),
+    ]
+
+    middlewares_resolvers = get_middleware_resolvers(middlewares)
+
+    def func():
+        # type: () -> None
+        return
+
+    chain_iter = middleware_chain(func, middlewares_resolvers, wrap_in_promise=True)
+
+    assert_stdout(capsys, "")
+
+    chain_iter()
+
+    expected_stdout = (
+        "resolve() called for middleware c\n"
+        "resolve() called for middleware b\n"
+        "resolve() called for middleware a\n"
+        "then() for a\n"
+        "then() for b\n"
+        "then() for c\n"
+    )
+    assert_stdout(capsys, expected_stdout)
+
+
+def assert_stdout(capsys, expected_stdout):
+    # type: (Any, str) -> None
+    captured = capsys.readouterr()
+    assert captured.out == expected_stdout