test: add tests for entity_extract module

Covers _extract_x_handles (8 cases), _extract_x_hashtags (5 cases),
_extract_subreddits (6 cases), and extract_entities integration (4 cases).
Follows existing test patterns from test_dedupe.py.

tests/test_entity_extract.py

@@ -0,0 +1,167 @@
+"""Tests for entity_extract module."""
+
+import sys
+import unittest
+from pathlib import Path
+
+# Add lib to path
+sys.path.insert(0, str(Path(__file__).parent.parent / "scripts"))
+
+from lib import entity_extract
+
+
+class TestExtractXHandles(unittest.TestCase):
+    def test_basic_author_handle(self):
+        items = [{"author_handle": "techguru", "text": ""}]
+        result = entity_extract._extract_x_handles(items)
+        self.assertEqual(result, ["techguru"])
+
+    def test_mentions_in_text(self):
+        items = [{"text": "Great thread by @airesearcher and @mldev"}]
+        result = entity_extract._extract_x_handles(items)
+        self.assertIn("airesearcher", result)
+        self.assertIn("mldev", result)
+
+    def test_generic_handles_filtered(self):
+        items = [
+            {"author_handle": "@openai", "text": ""},
+            {"author_handle": "@elonmusk", "text": ""},
+            {"author_handle": "realexpert", "text": ""},
+        ]
+        result = entity_extract._extract_x_handles(items)
+        self.assertEqual(result, ["realexpert"])
+
+    def test_case_normalization(self):
+        items = [{"author_handle": "@CamelCase", "text": ""}]
+        result = entity_extract._extract_x_handles(items)
+        self.assertEqual(result, ["camelcase"])
+
+    def test_frequency_ranking(self):
+        items = [
+            {"author_handle": "popular", "text": ""},
+            {"author_handle": "popular", "text": ""},
+            {"author_handle": "popular", "text": ""},
+            {"author_handle": "rare", "text": ""},
+        ]
+        result = entity_extract._extract_x_handles(items)
+        self.assertEqual(result[0], "popular")
+
+    def test_leading_at_stripped(self):
+        items = [{"author_handle": "@withatsign", "text": ""}]
+        result = entity_extract._extract_x_handles(items)
+        self.assertEqual(result, ["withatsign"])
+
+    def test_empty_input(self):
+        result = entity_extract._extract_x_handles([])
+        self.assertEqual(result, [])
+
+    def test_mixed_items(self):
+        items = [
+            {"author_handle": "poster1", "text": "Check @mentioned"},
+            {"text": "No author here"},
+            {"author_handle": "", "text": ""},
+        ]
+        result = entity_extract._extract_x_handles(items)
+        self.assertIn("poster1", result)
+        self.assertIn("mentioned", result)
+        self.assertEqual(len(result), 2)
+
+
+class TestExtractXHashtags(unittest.TestCase):
+    def test_basic_hashtag(self):
+        items = [{"text": "Exciting news #AI"}]
+        result = entity_extract._extract_x_hashtags(items)
+        self.assertEqual(result, ["#ai"])
+
+    def test_multiple_tags(self):
+        items = [{"text": "#Python and #MachineLearning are trending"}]
+        result = entity_extract._extract_x_hashtags(items)
+        self.assertIn("#python", result)
+        self.assertIn("#machinelearning", result)
+
+    def test_frequency_ranking(self):
+        items = [
+            {"text": "#ai is great"},
+            {"text": "#ai again"},
+            {"text": "#rare tag"},
+        ]
+        result = entity_extract._extract_x_hashtags(items)
+        self.assertEqual(result[0], "#ai")
+
+    def test_single_char_tag_filtered(self):
+        items = [{"text": "#X is not enough chars but #AI is"}]
+        result = entity_extract._extract_x_hashtags(items)
+        # #X is only 1 char, filtered by \w{2,30} regex
+        self.assertNotIn("#x", result)
+        self.assertIn("#ai", result)
+
+    def test_empty_input(self):
+        result = entity_extract._extract_x_hashtags([])
+        self.assertEqual(result, [])
+
+
+class TestExtractSubreddits(unittest.TestCase):
+    def test_basic_subreddit_field(self):
+        items = [{"subreddit": "MachineLearning"}]
+        result = entity_extract._extract_subreddits(items)
+        self.assertEqual(result, ["MachineLearning"])
+
+    def test_cross_ref_in_comment_insights(self):
+        items = [{"subreddit": "AI", "comment_insights": ["Check out r/localLLaMA for more"]}]
+        result = entity_extract._extract_subreddits(items)
+        self.assertIn("localLLaMA", result)
+
+    def test_cross_ref_in_top_comments(self):
+        items = [{"subreddit": "tech", "top_comments": [{"excerpt": "Also see r/programming"}]}]
+        result = entity_extract._extract_subreddits(items)
+        self.assertIn("programming", result)
+
+    def test_frequency_ranking(self):
+        items = [
+            {"subreddit": "popular"},
+            {"subreddit": "popular"},
+            {"subreddit": "rare"},
+        ]
+        result = entity_extract._extract_subreddits(items)
+        self.assertEqual(result[0], "popular")
+
+    def test_leading_r_slash_stripped(self):
+        items = [{"subreddit": "r/stripped"}]
+        result = entity_extract._extract_subreddits(items)
+        self.assertEqual(result, ["stripped"])
+
+    def test_empty_input(self):
+        result = entity_extract._extract_subreddits([])
+        self.assertEqual(result, [])
+
+
+class TestExtractEntities(unittest.TestCase):
+    def test_integration(self):
+        reddit = [{"subreddit": "AI", "comment_insights": ["r/localLLaMA"]}]
+        x = [{"author_handle": "researcher", "text": "#deeplearning @colleague"}]
+        result = entity_extract.extract_entities(reddit, x)
+        self.assertIn("researcher", result["x_handles"])
+        self.assertIn("#deeplearning", result["x_hashtags"])
+        self.assertIn("AI", result["reddit_subreddits"])
+
+    def test_max_limits(self):
+        x = [
+            {"author_handle": f"user{i}", "text": ""}
+            for i in range(10)
+        ]
+        result = entity_extract.extract_entities([], x, max_handles=2)
+        self.assertLessEqual(len(result["x_handles"]), 2)
+
+    def test_empty_inputs(self):
+        result = entity_extract.extract_entities([], [])
+        self.assertEqual(result["x_handles"], [])
+        self.assertEqual(result["x_hashtags"], [])
+        self.assertEqual(result["reddit_subreddits"], [])
+
+    def test_return_keys(self):
+        result = entity_extract.extract_entities([], [])
+        self.assertSetEqual(set(result.keys()), {"x_handles", "x_hashtags", "reddit_subreddits"})
+
+
+if __name__ == "__main__":
+    unittest.main()