test

public/app/core/utils/query.test.ts

+import { DataQuery } from '@grafana/ui';
+import { getNextRefIdChar } from './query';
+
+const dataQueries: DataQuery[] = [
+  {
+    refId: 'A',
+  },
+  {
+    refId: 'B',
+  },
+  {
+    refId: 'C',
+  },
+  {
+    refId: 'D',
+  },
+  {
+    refId: 'E',
+  },
+];
+
+describe('Get next refId char', () => {
+  it('should return next char', () => {
+    expect(getNextRefIdChar(dataQueries)).toEqual('F');
+  });
+
+  it('should get first char', () => {
+    expect(getNextRefIdChar([])).toEqual('A');
+  });
+});