Covering tag-related util function with tests

tests/lib/booru/tag-utils.spec.ts

@@ -0,0 +1,33 @@
+import { buildTagsAndAliasesMap } from "$lib/booru/tag-utils";
+
+describe('buildTagsAndAliasesMap', () => {
+  const exampleTag = 'safe';
+  const exampleTagAlias = 'rating:safe';
+  const tagsAndAliases = [exampleTag, exampleTagAlias, 'anthro', 'cat', 'feline', 'mammal', 'male', 'boy'];
+  const tagsOnly = [exampleTag, 'anthro', 'cat', 'feline', 'mammal', 'male'];
+  const mapping = buildTagsAndAliasesMap(tagsAndAliases, tagsOnly);
+
+  it('should return a map of tags', () => {
+    expect(mapping).toBeInstanceOf(Map);
+  });
+
+  it('should point aliases to their original tags', () => {
+    expect(mapping.get(exampleTagAlias)).toBe(exampleTag);
+  });
+
+  it('should point tags to themselves', () => {
+    expect(mapping.get(exampleTag)).toBe(exampleTag);
+  });
+
+  it('should ignore broken tag aliases and show a warning', () => {
+    vi.spyOn(console, 'warn');
+
+    const brokenMapping = buildTagsAndAliasesMap(
+      ['broken alias', 'tag1', 'tag2'],
+      ['tag1', 'tag2'],
+    );
+
+    expect(console.warn).toBeCalledTimes(1);
+    expect(brokenMapping.has('broken alias')).toBe(false);
+  });
+});