Autotiles are a new asset type with a tab that shows every tile of the floor (2x3) or wall (2x2) block and an animated sample pattern (#118)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/editor/autotile-strip.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+import { dropIndex } from '../../src/editor/autotile/PictureStrip';
+
+/**
+ * Reordering the pictures of an autotile by dragging a row (#118). The index the move command
+ * takes counts in the list without the dragged row, which is where the off-by-ones live.
+ */
+describe('dropping a picture row', () => {
+  it('takes the place of the row it is dropped on', () => {
+    expect(dropIndex(0, { at: 'onto', targetId: '1' }, 3)).toBe(1);
+    expect(dropIndex(2, { at: 'onto', targetId: '0' }, 3)).toBe(0);
+    // Dropping a row on itself is nothing to do – which is also what the list reports as no spot.
+    expect(dropIndex(1, { at: 'onto', targetId: '1' }, 3)).toBe(1);
+  });
+
+  it('counts a gap in the list the row has already left', () => {
+    // Downwards: the gap below row 1 is index 1 once row 0 is out of the way.
+    expect(dropIndex(0, { at: 'after', targetId: '1' }, 3)).toBe(1);
+    expect(dropIndex(0, { at: 'before', targetId: '2' }, 3)).toBe(1);
+    // Upwards nothing shifts: the gap above row 0 stays index 0.
+    expect(dropIndex(2, { at: 'before', targetId: '0' }, 3)).toBe(0);
+    expect(dropIndex(2, { at: 'after', targetId: '0' }, 3)).toBe(1);
+    expect(dropIndex(1, { at: 'end' }, 3)).toBe(2);
+  });
+
+  it('refuses a row or a target that is not in the list', () => {
+    expect(dropIndex(-1, { at: 'end' }, 3)).toBe(-1);
+    expect(dropIndex(3, { at: 'end' }, 3)).toBe(-1);
+    expect(dropIndex(0, { at: 'onto', targetId: '9' }, 3)).toBe(-1);
+    expect(dropIndex(0, { at: 'before', targetId: 'nonsense' }, 3)).toBe(-1);
+  });
+});