Fix TextSplitter.from_tiktoken(#4361)

Thanks to @danb27 for the fix! Minor update

Fixes https://github.com/hwchase17/langchain/issues/4357

---------

Co-authored-by: Dan Bianchini <42096328+danb27@users.noreply.github.com>

tests/integration_tests/test_text_splitter.py

@@ -23,19 +23,24 @@ def test_huggingface_tokenizer() -> None:
     assert output == ["foo", "bar"]
 
 
-class TestTokenTextSplitter:
-    """Test token text splitter."""
+def test_token_text_splitter() -> None:
+    """Test no overlap."""
+    splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=0)
+    output = splitter.split_text("abcdef" * 5)  # 10 token string
+    expected_output = ["abcdefabcdefabc", "defabcdefabcdef"]
+    assert output == expected_output
 
-    def test_basic(self) -> None:
-        """Test no overlap."""
-        splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=0)
-        output = splitter.split_text("abcdef" * 5)  # 10 token string
-        expected_output = ["abcdefabcdefabc", "defabcdefabcdef"]
-        assert output == expected_output
 
-    def test_overlap(self) -> None:
-        """Test with overlap."""
-        splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=1)
-        output = splitter.split_text("abcdef" * 5)  # 10 token string
-        expected_output = ["abcdefabcdefabc", "abcdefabcdefabc", "abcdef"]
-        assert output == expected_output
+def test_token_text_splitter_overlap() -> None:
+    """Test with overlap."""
+    splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=1)
+    output = splitter.split_text("abcdef" * 5)  # 10 token string
+    expected_output = ["abcdefabcdefabc", "abcdefabcdefabc", "abcdef"]
+    assert output == expected_output
+
+
+def test_token_text_splitter_from_tiktoken() -> None:
+    splitter = TokenTextSplitter.from_tiktoken_encoder(model_name="gpt-3.5-turbo")
+    expected_tokenizer = "cl100k_base"
+    actual_tokenizer = splitter._tokenizer.name
+    assert expected_tokenizer == actual_tokenizer