utils: validateDirectiveConfig initial draft

src/index.js

@@ -0,0 +1,7 @@
+const createDirective = require("./create-directive");
+const createSchemaDirective = require("./create-schema-directives");
+
+module.exports = {
+  createDirective,
+  createSchemaDirective,
+};

src/utils.js

@@ -0,0 +1,25 @@
+const validateDirectiveConfig = (directiveConfig) => {
+  const { name, resolverReplacer } = directiveConfig;
+
+  let message;
+  if (!name || !resolverReplacer) {
+    message = "directiveConfig.name is required";
+  } else if (!resolverReplacer) {
+    message = "directiveConfig.resolverReplacer is required";
+  } else if (typeof name !== "string") {
+    message = "directiveConfig.name must be a string";
+  } else if (typeof resolverReplacer !== "function") {
+    message = "directiveConfig.resolverReplacer must be a function";
+  } else {
+    return directiveConfig;
+  }
+
+  const error = new Error(message);
+  error.name = "CreateDirectiveError";
+
+  throw error;
+};
+
+module.exports = {
+  validateDirectiveConfig,
+};