Add tests to cover PlaceholdersBuffer and sum hint

Related: #13615

public/app/features/explore/PlaceholdersBuffer.test.ts

+import PlaceholdersBuffer from './PlaceholdersBuffer';
+
+describe('PlaceholdersBuffer', () => {
+  it('does nothing if no placeholders are defined', () => {
+    const text = 'metric';
+    const buffer = new PlaceholdersBuffer(text);
+
+    expect(buffer.hasPlaceholders()).toBe(false);
+    expect(buffer.toString()).toBe(text);
+    expect(buffer.getNextMoveOffset()).toBe(0);
+  });
+
+  it('respects the traversal order of placeholders', () => {
+    const text = 'sum($2 offset $1) by ($3)';
+    const buffer = new PlaceholdersBuffer(text);
+
+    expect(buffer.hasPlaceholders()).toBe(true);
+    expect(buffer.toString()).toBe('sum( offset ) by ()');
+    expect(buffer.getNextMoveOffset()).toBe(12);
+
+    buffer.setNextPlaceholderValue('1h');
+
+    expect(buffer.hasPlaceholders()).toBe(true);
+    expect(buffer.toString()).toBe('sum( offset 1h) by ()');
+    expect(buffer.getNextMoveOffset()).toBe(-10);
+
+    buffer.setNextPlaceholderValue('metric');
+
+    expect(buffer.hasPlaceholders()).toBe(true);
+    expect(buffer.toString()).toBe('sum(metric offset 1h) by ()');
+    expect(buffer.getNextMoveOffset()).toBe(16);
+
+    buffer.setNextPlaceholderValue('label');
+
+    expect(buffer.hasPlaceholders()).toBe(false);
+    expect(buffer.toString()).toBe('sum(metric offset 1h) by (label)');
+    expect(buffer.getNextMoveOffset()).toBe(0);
+  });
+
+  it('respects the traversal order of adjacent placeholders', () => {
+    const text = '$1$3$2$4';
+    const buffer = new PlaceholdersBuffer(text);
+
+    expect(buffer.hasPlaceholders()).toBe(true);
+    expect(buffer.toString()).toBe('');
+    expect(buffer.getNextMoveOffset()).toBe(0);
+
+    buffer.setNextPlaceholderValue('1');
+
+    expect(buffer.hasPlaceholders()).toBe(true);
+    expect(buffer.toString()).toBe('1');
+    expect(buffer.getNextMoveOffset()).toBe(0);
+
+    buffer.setNextPlaceholderValue('2');
+
+    expect(buffer.hasPlaceholders()).toBe(true);
+    expect(buffer.toString()).toBe('12');
+    expect(buffer.getNextMoveOffset()).toBe(-1);
+
+    buffer.setNextPlaceholderValue('3');
+
+    expect(buffer.hasPlaceholders()).toBe(true);
+    expect(buffer.toString()).toBe('132');
+    expect(buffer.getNextMoveOffset()).toBe(1);
+
+    buffer.setNextPlaceholderValue('4');
+
+    expect(buffer.hasPlaceholders()).toBe(false);
+    expect(buffer.toString()).toBe('1324');
+    expect(buffer.getNextMoveOffset()).toBe(0);
+  });
+});

public/app/plugins/datasource/prometheus/specs/query_hints.test.ts

-import { getQueryHints } from '../query_hints';
+import { getQueryHints, SUM_HINT_THRESHOLD_COUNT } from '../query_hints';
 
 describe('getQueryHints()', () => {
   it('returns no hints for no series', () => {
@@ -79,4 +79,23 @@ describe('getQueryHints()', () => {
       },
     });
   });
+
+  it('returns a sum hint when many time series results are returned for a simple metric', () => {
+    const seriesCount = SUM_HINT_THRESHOLD_COUNT;
+    const series = Array.from({ length: seriesCount }, _ => ({
+      datapoints: [[0, 0], [0, 0]],
+    }));
+    const hints = getQueryHints('metric', series);
+    expect(hints.length).toBe(seriesCount);
+    expect(hints[0]).toMatchObject({
+      label: 'Many time series results returned.',
+      index: 0,
+      fix: {
+        action: {
+          type: 'ADD_SUM',
+          query: 'metric',
+        },
+      },
+    });
+  });
 });