Utilize pipelining of grep_search -> read_file to eliminate turns (#19574)

packages/core/src/tools/diff-utils.test.ts

@@ -0,0 +1,66 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, expect, it } from 'vitest';
+import { getDiffContextSnippet } from './diff-utils.js';
+
+describe('getDiffContextSnippet', () => {
+  it('should return the whole new content if originalContent is empty', () => {
+    const original = '';
+    const modified = 'line1\nline2\nline3';
+    expect(getDiffContextSnippet(original, modified)).toBe(modified);
+  });
+
+  it('should return the whole content if there are no changes', () => {
+    const content = 'line1\nline2\nline3';
+    expect(getDiffContextSnippet(content, content)).toBe(content);
+  });
+
+  it('should show added lines with context', () => {
+    const original = '1\n2\n3\n4\n5\n6\n7\n8\n9\n10';
+    const modified = '1\n2\n3\n4\n5\nadded\n6\n7\n8\n9\n10';
+    // Default context is 5 lines.
+    expect(getDiffContextSnippet(original, modified)).toBe(modified);
+  });
+
+  it('should use ellipses for changes far apart', () => {
+    const original = Array.from({ length: 20 }, (_, i) => `${i + 1}`).join(
+      '\n',
+    );
+    const modified = original
+      .replace('2\n', '2\nadded1\n')
+      .replace('19', '19\nadded2');
+    const snippet = getDiffContextSnippet(original, modified, 2);
+
+    expect(snippet).toContain('1\n2\nadded1\n3\n4');
+    expect(snippet).toContain('...');
+    expect(snippet).toContain('18\n19\nadded2\n20');
+  });
+
+  it('should respect custom contextLines', () => {
+    const original = '1\n2\n3\n4\n5\n6\n7\n8\n9\n10';
+    const modified = '1\n2\n3\n4\n5\nadded\n6\n7\n8\n9\n10';
+    const snippet = getDiffContextSnippet(original, modified, 1);
+
+    expect(snippet).toBe('...\n5\nadded\n6\n...');
+  });
+
+  it('should handle multiple changes close together by merging ranges', () => {
+    const original = '1\n2\n3\n4\n5\n6\n7\n8\n9\n10';
+    const modified = '1\nadded1\n2\nadded2\n3\n4\n5\n6\n7\n8\n9\n10';
+    const snippet = getDiffContextSnippet(original, modified, 1);
+
+    expect(snippet).toBe('1\nadded1\n2\nadded2\n3\n...');
+  });
+
+  it('should handle removals', () => {
+    const original = '1\n2\n3\n4\n5\n6\n7\n8\n9\n10';
+    const modified = '1\n2\n3\n4\n6\n7\n8\n9\n10';
+    const snippet = getDiffContextSnippet(original, modified, 1);
+
+    expect(snippet).toBe('...\n4\n6\n...');
+  });
+});