test(json-crdt-extensions): 💍 add .prevId() edge case tests

Author: streamich

src/json-crdt-extensions/peritext/point/Point.ts

@@ -171,13 +171,11 @@ export class Point implements Pick<Stateful, 'refresh'>, Printable {
    *          such character.
    */
   public prevId(move: number = 1): ITimestampStruct | undefined {
-    // TODO: add tests for when cursor is at the start.
     if (this.isStartOfStr()) return;
     let remaining: number = move;
     const {id, txt} = this;
     const str = txt.str;
     let chunk = this.chunk();
-    // TODO: handle case when cursor starts from end of string.
     if (!chunk) return str.id;
     if (!chunk.del) {
       const offset = id.time - chunk.id.time;

src/json-crdt-extensions/peritext/point/__tests__/Point.spec.ts

@@ -539,6 +539,28 @@ describe('.prevId()', () => {
     p2.nextId(0);
     expect(p2.rightChar()!.view()).toBe('4');
   });
+
+  test('returns undefined, when at start of str', () => {
+    const {peritext} = setupWithChunkedText();
+    const point = peritext.pointAtStart();
+    expect(point.prevId()).toBe(undefined);
+  });
+
+  test('returns undefined, when at first char', () => {
+    const {peritext} = setupWithChunkedText();
+    const point1 = peritext.pointAt(0, Anchor.Before);
+    const point2 = peritext.pointAt(0, Anchor.After);
+    expect(point1.prevId()).toBe(undefined);
+    expect(point2.prevId()).toBe(undefined);
+  });
+
+  test('returns last char, when at end of str', () => {
+    const {peritext} = setupWithChunkedText();
+    const point1 = peritext.pointAtEnd();
+    const point2 = peritext.pointAt(9, Anchor.Before);
+    const id = point1.prevId();
+    expect(id).toEqual(point2.id);
+  });
 });
 
 describe('.rightChar()', () => {