feat(stats): add v1 immersion stats dashboard (#19)

stats/src/lib/vocabulary-tab.test.ts

@@ -0,0 +1,34 @@
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import test from 'node:test';
+import { fileURLToPath } from 'node:url';
+
+const VOCABULARY_TAB_PATH = fileURLToPath(
+  new URL('../components/vocabulary/VocabularyTab.tsx', import.meta.url),
+);
+
+test('VocabularyTab declares all hooks before loading and error early returns', () => {
+  const source = fs.readFileSync(VOCABULARY_TAB_PATH, 'utf8');
+  const loadingGuardIndex = source.indexOf('if (loading) {');
+
+  assert.notEqual(loadingGuardIndex, -1, 'expected loading early return');
+
+  const hooksAfterLoadingGuard = source
+    .slice(loadingGuardIndex)
+    .match(/\buse(?:State|Effect|Memo|Callback|Ref|Reducer)\s*\(/g);
+
+  assert.deepEqual(hooksAfterLoadingGuard ?? [], []);
+});
+
+test('VocabularyTab memoizes summary and known-word aggregate calculations', () => {
+  const source = fs.readFileSync(VOCABULARY_TAB_PATH, 'utf8');
+
+  assert.match(
+    source,
+    /const summary = useMemo\([\s\S]*buildVocabularySummary\(filteredWords, kanji\)[\s\S]*\[filteredWords, kanji\][\s\S]*\);/,
+  );
+  assert.match(
+    source,
+    /const knownWordCount = useMemo\(\(\) => \{[\s\S]*for \(const w of filteredWords\) \{[\s\S]*knownWords\.has\(w\.headword\)[\s\S]*\}\s*return count;\s*\}, \[filteredWords, knownWords\]\);/,
+  );
+});