Add optional schema compiler error messages

tools/json_schema_compiler/test/error_generation.json

Index: tools/json_schema_compiler/test/error_generation.json
diff --git a/tools/json_schema_compiler/test/error_generation.json b/tools/json_schema_compiler/test/error_generation.json
new file mode 100644
index 0000000000000000000000000000000000000000..884e26f2521038b04e340317d5897443091a5e1f
--- /dev/null
+++ b/tools/json_schema_compiler/test/error_generation.json
@@ -0,0 +1,106 @@
+[
+  {
+    "namespace": "error_generation",
+    "description": "Generates ALL the errors.",
+    "compiler_options": {
+      "generate_error_messages": true
+    },
+    "types": [
+      {
+        "id": "TestType",
+        "type": "object",
+        "properties": {
+          "string": {
+            "type": "string",
+            "description": "Some string."
+          }
+        }
+      },
+      {
+        "id": "ChoiceType",
+        "type": "object",
+        "properties": {
+          "integers": {
+            "choices": [
+               {"type": "array", "items": {"type": "integer", "minimum": 0}},
+               {"type": "integer"}
+            ]
+          }
+        }
+      },
+      {
+        "id": "ObjectType",
+        "type": "object",
+        "properties": {
+          "otherType": {
+            "$ref": "error_generation.TestType",
+            "optional": true
+          }
+        }
+      },
+      {
+        "id": "Enumeration",
+        "type": "string",
+        "enum": ["one", "two", "three"]
+      },
+      {
+        "id": "HasEnumeration",
+        "type": "object",
+        "properties": {
+          "enumeration": {
+            "$ref": "Enumeration"
+          }
+        }
+      },
+      {
+        "id": "BinaryData",
+        "type": "object",
+        "properties": {
+          "data": {
+            "type" : "binary"
+          }
+        }
+      }
+    ],
+    "functions": [
+      {
+        "name": "testString",
+        "type": "function",
+        "description": "Takes a string. Or not.",
+        "parameters": [
+          {
+            "name": "str",
+            "type": "string",
+            "optional": true
+          }
+        ]
+      },
+      {
+        "name": "testFunction",
+        "type": "function",
+        "description": "Specifies a number of parameters.",
+        "parameters": [
+          {
+            "name": "num",
+            "type": "integer"
+          }
+        ]
+      },
+      {
+        "name": "testTypeInObject",
+        "type": "function",
+        "description": "Takes a TestType.",
+        "parameters": [
+          {
+            "name": "paramObject",
+            "type": "object",
+            "properties": {
+              "testType": {"$ref": "error_generation.TestType", "optional": true},
+              "boolean": {"type": "boolean"}
+            }
+          }
+        ]
+      }
+    ]
+  }
+]