1 files changed, 129 insertions, 0 deletions
diff --git a/packages/core/src/tools/diffOptions.test.ts b/packages/core/src/tools/diffOptions.test.ts
new file mode 100644
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+++ b/packages/core/src/tools/diffOptions.test.ts
@@ -0,0 +1,129 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, expect, it } from 'vitest';
+import { getDiffStat } from './diffOptions.js';
+
+describe('getDiffStat', () => {
+  const fileName = 'test.txt';
+
+  it('should return 0 for all stats when there are no changes', () => {
+    const oldStr = 'line1\nline2\n';
+    const aiStr = 'line1\nline2\n';
+    const userStr = 'line1\nline2\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 0,
+      ai_removed_lines: 0,
+      user_added_lines: 0,
+      user_removed_lines: 0,
+    });
+  });
+
+  it('should correctly report AI additions', () => {
+    const oldStr = 'line1\nline2\n';
+    const aiStr = 'line1\nline2\nline3\n';
+    const userStr = 'line1\nline2\nline3\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 1,
+      ai_removed_lines: 0,
+      user_added_lines: 0,
+      user_removed_lines: 0,
+    });
+  });
+
+  it('should correctly report AI removals', () => {
+    const oldStr = 'line1\nline2\nline3\n';
+    const aiStr = 'line1\nline3\n';
+    const userStr = 'line1\nline3\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 0,
+      ai_removed_lines: 1,
+      user_added_lines: 0,
+      user_removed_lines: 0,
+    });
+  });
+
+  it('should correctly report AI modifications', () => {
+    const oldStr = 'line1\nline2\nline3\n';
+    const aiStr = 'line1\nline_two\nline3\n';
+    const userStr = 'line1\nline_two\nline3\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 1,
+      ai_removed_lines: 1,
+      user_added_lines: 0,
+      user_removed_lines: 0,
+    });
+  });
+
+  it('should correctly report user additions', () => {
+    const oldStr = 'line1\nline2\n';
+    const aiStr = 'line1\nline2\nline3\n';
+    const userStr = 'line1\nline2\nline3\nline4\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 1,
+      ai_removed_lines: 0,
+      user_added_lines: 1,
+      user_removed_lines: 0,
+    });
+  });
+
+  it('should correctly report user removals', () => {
+    const oldStr = 'line1\nline2\n';
+    const aiStr = 'line1\nline2\nline3\n';
+    const userStr = 'line1\nline2\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 1,
+      ai_removed_lines: 0,
+      user_added_lines: 0,
+      user_removed_lines: 1,
+    });
+  });
+
+  it('should correctly report user modifications', () => {
+    const oldStr = 'line1\nline2\n';
+    const aiStr = 'line1\nline2\nline3\n';
+    const userStr = 'line1\nline2\nline_three\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 1,
+      ai_removed_lines: 0,
+      user_added_lines: 1,
+      user_removed_lines: 1,
+    });
+  });
+
+  it('should handle complex changes from both AI and user', () => {
+    const oldStr = 'line1\nline2\nline3\nline4\n';
+    const aiStr = 'line_one\nline2\nline_three\nline4\n';
+    const userStr = 'line_one\nline_two\nline_three\nline4\nline5\n';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 2,
+      ai_removed_lines: 2,
+      user_added_lines: 2,
+      user_removed_lines: 1,
+    });
+  });
+
+  it('should report a single line modification as one addition and one removal', () => {
+    const oldStr = 'hello world';
+    const aiStr = 'hello universe';
+    const userStr = 'hello universe';
+    const diffStat = getDiffStat(fileName, oldStr, aiStr, userStr);
+    expect(diffStat).toEqual({
+      ai_added_lines: 1,
+      ai_removed_lines: 1,
+      user_added_lines: 0,
+      user_removed_lines: 0,
+    });
+  });
+});