diff --git a/nextlinegraphql/plugins/dev/graphql/__init__.py b/nextlinegraphql/plugins/dev/graphql/__init__.py
new file mode 100644
index 0000000..091987e
--- /dev/null
+++ b/nextlinegraphql/plugins/dev/graphql/__init__.py
@@ -0,0 +1,19 @@
+from pathlib import Path
+
+from graphql import parse, print_ast
+
+
+def read_gql(path: Path | str) -> str:
+    '''Load a GraphQL query from a file while checking its syntax.'''
+
+    text = Path(path).read_text()
+    parsed = parse(text)
+    reformatted = print_ast(parsed)
+    return reformatted
+
+
+pwd = Path(__file__).resolve().parent
+
+
+sub = pwd / 'queries'
+QUERY_HEADERS = read_gql(sub / 'Headers.gql')
diff --git a/nextlinegraphql/plugins/dev/graphql/queries/Headers.gql b/nextlinegraphql/plugins/dev/graphql/queries/Headers.gql
new file mode 100644
index 0000000..bd292ff
--- /dev/null
+++ b/nextlinegraphql/plugins/dev/graphql/queries/Headers.gql
@@ -0,0 +1,5 @@
+query DevHeaders {
+  dev {
+    headers
+  }
+}
\ No newline at end of file
diff --git a/nextlinegraphql/plugins/dev/schema/__init__.py b/nextlinegraphql/plugins/dev/schema/__init__.py
index f177b73..64e8218 100644
--- a/nextlinegraphql/plugins/dev/schema/__init__.py
+++ b/nextlinegraphql/plugins/dev/schema/__init__.py
@@ -1,3 +1,6 @@
 __all__ = ['Query']
 
 from .query import Query
+
+Mutation = None
+Subscription = None
diff --git a/tests/plugins/ctrl/schema/test_run.py b/tests/plugins/ctrl/schema/test_run.py
index a6572b0..a7297f6 100644
--- a/tests/plugins/ctrl/schema/test_run.py
+++ b/tests/plugins/ctrl/schema/test_run.py
@@ -100,7 +100,7 @@ async def _subscribe_state(schema: Schema, context: Any) -> list[str]:
     ret = []
     sub = await schema.subscribe(SUBSCRIBE_STATE, context_value=context)
     assert hasattr(sub, '__aiter__')
-    async for result in sub:
+    async for result in sub:  # pragma: no branch
         assert (data := result.data)
         state = data['ctrlState']
         ret.append(state)
@@ -138,7 +138,7 @@ async def _control_execution(schema: Schema, context: Any) -> None:
     agen = agen_with_wait(sub)
 
     prev_ids = set[int]()
-    async for result in agen:
+    async for result in agen:  # pragma: no branch
         assert isinstance(result, ExecutionResult)
         assert (data := result.data)
         trace_ids: list[int] = data['ctrlTraceIds']
diff --git a/tests/plugins/dev/__init__.py b/tests/plugins/dev/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/plugins/dev/schema/__init__.py b/tests/plugins/dev/schema/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/plugins/dev/schema/conftest.py b/tests/plugins/dev/schema/conftest.py
new file mode 100644
index 0000000..4e3db38
--- /dev/null
+++ b/tests/plugins/dev/schema/conftest.py
@@ -0,0 +1,14 @@
+import pytest
+from strawberry import Schema
+
+from nextlinegraphql.plugins.dev.schema import Mutation, Query, Subscription
+
+
+@pytest.fixture(scope='session')
+def schema() -> Schema:
+    '''GraphQL schema
+
+    The scope is `session` because Hypothesis doesn't allow function-scoped
+    fixtures. This is fine as the schema is stateless.
+    '''
+    return Schema(query=Query, mutation=Mutation, subscription=Subscription)
diff --git a/tests/plugins/dev/schema/queries/__init__.py b/tests/plugins/dev/schema/queries/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/plugins/dev/schema/queries/test_headers.py b/tests/plugins/dev/schema/queries/test_headers.py
new file mode 100644
index 0000000..3a14e87
--- /dev/null
+++ b/tests/plugins/dev/schema/queries/test_headers.py
@@ -0,0 +1,18 @@
+import json
+from unittest.mock import Mock
+
+from starlette.requests import Headers, Request
+
+from nextlinegraphql.plugins.dev.graphql import QUERY_HEADERS
+from tests.plugins.dev.schema.conftest import Schema
+
+
+async def test_schema(schema: Schema) -> None:
+    request = Mock(spec=Request)
+    request.headers = Headers({'foo': 'bar'})
+    context = {'request': request}
+    result = await schema.execute(QUERY_HEADERS, context_value=context)
+    assert (data := result.data)
+    expected = {'dev': {'headers': json.dumps({'foo': 'bar'})}}
+    assert data == expected
+