test(util): 💍 add failing sfx() test

Author: streamich

packages/json-joy/src/util/diff/__tests__/str.spec.ts

@@ -1,6 +1,37 @@
-import {PATCH_OP_TYPE, type Patch, diff, diffEdit, overlap, normalize, apply, src, dst, invert} from '../str';
+import {PATCH_OP_TYPE, type Patch, diff, diffEdit, overlap, normalize, apply, src, dst, invert, pfx, sfx} from '../str';
 import {assertPatch} from './util';
 
+describe('pfx()', () => {
+  test('finds common prefixes', () => {
+    expect(pfx('abc', 'b')).toEqual(0);
+    expect(pfx('abc', 'a')).toEqual(1);
+    expect(pfx('abc', 'ab')).toEqual(2);
+    expect(pfx('abc', 'abc')).toEqual(3);
+    expect(pfx('abc', 'abcd')).toEqual(3);
+    expect(pfx('abc', 'abcde')).toEqual(3);
+    expect(pfx('👨‍🍳', '👨‍🍳')).toEqual(5);
+    expect(pfx('👨‍🍳', '👨‍🍳chef')).toEqual(5);
+    expect(pfx('👨‍🍳chef', '👨‍🍳')).toEqual(5);
+    expect(pfx('👨‍🍳👨‍🍳', '👨‍🍳')).toEqual(5);
+    expect('👨‍🍳chef'.slice(0, 5)).toBe('👨‍🍳');
+  });
+});
+
+describe('sfx()', () => {
+  test('finds common suffixes', () => {
+    expect(sfx('abc', 'b')).toEqual(0);
+    expect(sfx('abc', 'c')).toEqual(1);
+    expect(sfx('abc', 'bc')).toEqual(2);
+    expect(sfx('abc', 'abc')).toEqual(3);
+    expect(sfx('abc', '_abc')).toEqual(3);
+    expect(sfx('abc', 'abcd')).toEqual(0);
+    expect(sfx('👨‍🍳', '👨‍🍳')).toEqual(5);
+    // expect(sfx('👨‍🍳', '👨‍🍳chef')).toEqual(5);
+    // expect(sfx('👨‍🍳chef', '👨‍🍳')).toEqual(5);
+    // expect(sfx('👨‍🍳👨‍🍳', '👨‍🍳')).toEqual(5);
+  });
+});
+
 describe('normalize()', () => {
   test('joins consecutive same type operations', () => {
     expect(

packages/json-joy/src/util/diff/str.ts

@@ -388,7 +388,7 @@ const diffNoCommonAffix = (src: string, dst: string): Patch => {
  * @param txt2 Second string.
  * @return The number of characters common to the start of each string.
  */
-export const pfx = (txt1: string, txt2: string) => {
+export const pfx = (txt1: string, txt2: string): number => {
   if (!txt1 || !txt2 || txt1.charAt(0) !== txt2.charAt(0)) return 0;
   let min = 0;
   let max = Math.min(txt1.length, txt2.length);