test: add test for enum type checking

_testdata/negative/wrong_enum_type/string_value.json

@@ -0,0 +1,30 @@
+{
+    "openapi": "3.0.3",
+    "info": {
+        "title": "title",
+        "version": "v0.1.0"
+    },
+    "paths": {
+        "/foo": {
+            "get": {
+                "responses": {
+                    "200": {
+                        "description": "User info",
+                        "content": {
+                            "application/json": {
+                                "schema": {
+                                    "type": "integer",
+                                    "enum": [
+                                        "1",
+                                        "2",
+                                        "3"
+                                    ]
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}