Modify output for wikipedia api wrapper (#2287)

## Description
Thanks for the quick maintenance for great repository!!
I modified wikipedia api wrapper

## Details
- Add output for missing search results
- Add tests

langchain/utilities/wikipedia.py

@@ -39,7 +39,10 @@ class WikipediaAPIWrapper(BaseModel):
         """Run Wikipedia search and get page summaries."""
         search_results = self.wiki_client.search(query)
         summaries = []
-        for i in range(min(self.top_k_results, len(search_results))):
+        len_search_results = len(search_results)
+        if len_search_results == 0:
+            return "No good Wikipedia Search Result was found"
+        for i in range(min(self.top_k_results, len_search_results)):
             summary = self.fetch_formatted_page_summary(search_results[i])
             if summary is not None:
                 summaries.append(summary)

tests/integration_tests/test_wikipedia_api.py

@@ -0,0 +1,19 @@
+"""Integration test for Wikipedia API Wrapper."""
+from langchain.utilities import WikipediaAPIWrapper
+
+
+def test_call() -> None:
+    """Test that WikipediaAPIWrapper returns correct answer"""
+
+    wikipedia = WikipediaAPIWrapper()
+    output = wikipedia.run("HUNTER X HUNTER")
+    assert "Yoshihiro Togashi" in output
+
+
+def test_no_result_call() -> None:
+    """Test that call gives no result."""
+    wikipedia = WikipediaAPIWrapper()
+    output = wikipedia.run(
+        "NORESULTCALL_NORESULTCALL_NORESULTCALL_NORESULTCALL_NORESULTCALL_NORESULTCALL"
+    )
+    assert "No good Wikipedia Search Result was found" == output