deleting a material is rejected if it is referenced by a sample

src/test/loadDev.ts

@@ -0,0 +1,12 @@
+import db from '../db';
+
+db.connect('dev', () => {
+  console.info('dropping data...');
+  db.drop(() => {  // reset database
+    console.info('loading data...');
+    db.loadJson(require('./db.json'), () => {
+      console.info('done');
+      process.exit(0);
+    });
+  });
+});