validates missing useAsTitle

src/collections/validate.js

@@ -1,12 +1,19 @@
 const errors = require('../errors');
 
-const { DuplicateCollection, MissingCollectionLabel } = errors;
+const { DuplicateCollection, MissingCollectionLabel, MissingUseAsTitle } = errors;
 
 module.exports = function validateCollection(collection, collections) {
   if (!collection.labels.singular) {
     throw new MissingCollectionLabel(collection);
   }
 
+  const { useAsTitle } = collection;
+  const fieldToUseAsTitle = collection.fields.find(field => useAsTitle === field.name);
+
+  if (!fieldToUseAsTitle) {
+    throw new MissingUseAsTitle(collection);
+  }
+
   if (collections && collections[collection.labels.singular]) {
     throw new DuplicateCollection(collection);
   }

src/errors/MissingUseAsTitle.js

@@ -0,0 +1,9 @@
+const APIError = require('./APIError');
+
+class MissingUseAsTitle extends APIError {
+  constructor(collection) {
+    super(`${collection.labels.singular} collection is missing a useAsTitle property.`);
+  }
+}
+
+module.exports = MissingCollectionLabel;