fix: Generation of invalid headers in some cases

Ref: #1142

docs/changelog.rst

@@ -13,6 +13,7 @@ Changelog
 **Fixed**
 
 - Pass ``data_generation_method`` to ``Case`` for GraphQL schemas.
+- Generation of invalid headers in some cases. `#1142`_
 
 `3.10.1`_ - 2021-10-04
 ----------------------
@@ -2183,6 +2184,7 @@ Deprecated
 .. _#1160: https://github.com/schemathesis/schemathesis/issues/1160
 .. _#1153: https://github.com/schemathesis/schemathesis/issues/1153
 .. _#1152: https://github.com/schemathesis/schemathesis/issues/1152
+.. _#1142: https://github.com/schemathesis/schemathesis/issues/1142
 .. _#1134: https://github.com/schemathesis/schemathesis/issues/1134
 .. _#1121: https://github.com/schemathesis/schemathesis/issues/1121
 .. _#1100: https://github.com/schemathesis/schemathesis/issues/1100

src/schemathesis/specs/openapi/_hypothesis.py

@@ -279,7 +279,7 @@ def get_parameters_strategy(
             "query": is_valid_query,
         }[location]
         # Headers with special format do not need filtration
-        if not (is_header_location(location) and _has_header_format(schema)):
+        if not (is_header_location(location) and _can_skip_header_filter(schema)):
             strategy = strategy.filter(filter_func)
         # Path & query parameters will be cast to string anyway, but having their JSON equivalents for
         # `True` / `False` / `None` improves chances of them passing validation in apps that expect boolean / null types
@@ -328,11 +328,9 @@ def make_positive_strategy(
     return from_schema(schema, custom_formats=STRING_FORMATS)
 
 
-def _has_header_format(schema: Dict[str, Any]) -> bool:
-    for sub_schema in schema.get("properties", {}).values():
-        if sub_schema.get("format") == HEADER_FORMAT:
-            return True
-    return False
+def _can_skip_header_filter(schema: Dict[str, Any]) -> bool:
+    # All headers should contain HEADER_FORMAT in order to avoid header filter
+    return all(sub_schema.get("format") == HEADER_FORMAT for sub_schema in schema.get("properties", {}).values())
 
 
 def make_negative_strategy(

test/specs/openapi/test_hypothesis.py

@@ -284,9 +284,8 @@ def test_header_filtration_not_needed(empty_open_api_3_schema, mocker):
     schema = schemathesis.from_dict(empty_open_api_3_schema)
 
     @given(schema["/data"]["GET"].as_strategy())
-    @settings(max_examples=1)
-    def test(_):
-        pass
+    def test(case):
+        assert is_valid_header(case.headers)
 
     test()
 
@@ -312,6 +311,45 @@ def test(_):
     mocked.assert_called()
 
 
+def test_missing_header_filter(empty_open_api_3_schema, mocker):
+    # Regression. See GH-1142
+    mocked = mocker.spy(_hypothesis, "is_valid_header")
+    # When some header parameters have the `format` keyword
+    # And some don't
+    empty_open_api_3_schema["paths"] = {
+        "/data": {
+            "get": {
+                "parameters": [
+                    {
+                        "name": "key1",
+                        "in": "header",
+                        "required": True,
+                        "schema": {"type": "string", "format": "uuid"},
+                    },
+                    {
+                        "name": "key2",
+                        "in": "header",
+                        "required": True,
+                        "schema": {"type": "string"},
+                    },
+                ],
+                "responses": {"200": {"description": "OK"}},
+            }
+        }
+    }
+
+    schema = schemathesis.from_dict(empty_open_api_3_schema)
+
+    @given(schema["/data"]["GET"].as_strategy())
+    def test(case):
+        assert is_valid_header(case.headers)
+
+    test()
+
+    # Then header filter should be used
+    mocked.assert_called()
+
+
 @pytest.mark.parametrize(
     "value, expected",
     (