Update Vertex AI to include Gemini (#14670)

h/t to @lkuligin 
-  **Description:** added new models on VertexAI
  - **Twitter handle:** @lkuligin

---------

Co-authored-by: Leonid Kuligin <lkuligin@yandex.ru>
Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

libs/community/tests/integration_tests/llms/test_vertexai.py

@@ -13,15 +13,33 @@ from langchain_core.outputs import LLMResult
 
 from langchain_community.llms import VertexAI, VertexAIModelGarden
 
+model_names_to_test = ["text-bison@001", "gemini-pro"]
+model_names_to_test_with_default = [None] + model_names_to_test
 
-def test_vertex_initialization() -> None:
-    llm = VertexAI()
+
+@pytest.mark.parametrize(
+    "model_name",
+    model_names_to_test_with_default,
+)
+def test_vertex_initialization(model_name: str) -> None:
+    llm = VertexAI(model_name=model_name) if model_name else VertexAI()
     assert llm._llm_type == "vertexai"
-    assert llm.model_name == llm.client._model_id
+    try:
+        assert llm.model_name == llm.client._model_id
+    except AttributeError:
+        assert llm.model_name == llm.client._model_name.split("/")[-1]
 
 
-def test_vertex_call() -> None:
-    llm = VertexAI(temperature=0)
+@pytest.mark.parametrize(
+    "model_name",
+    model_names_to_test_with_default,
+)
+def test_vertex_call(model_name: str) -> None:
+    llm = (
+        VertexAI(model_name=model_name, temperature=0)
+        if model_name
+        else VertexAI(temperature=0.0)
+    )
     output = llm("Say foo:")
     assert isinstance(output, str)
 
@@ -52,8 +70,16 @@ async def test_vertex_agenerate() -> None:
 
 
 @pytest.mark.scheduled
-def test_vertex_stream() -> None:
-    llm = VertexAI(temperature=0)
+@pytest.mark.parametrize(
+    "model_name",
+    model_names_to_test_with_default,
+)
+def test_vertex_stream(model_name: str) -> None:
+    llm = (
+        VertexAI(temperature=0, model_name=model_name)
+        if model_name
+        else VertexAI(temperature=0)
+    )
     outputs = list(llm.stream("Please say foo:"))
     assert isinstance(outputs[0], str)
 
@@ -145,7 +171,11 @@ async def test_model_garden_agenerate(
     assert len(output.generations) == 2
 
 
-def test_vertex_call_count_tokens() -> None:
-    llm = VertexAI()
+@pytest.mark.parametrize(
+    "model_name",
+    model_names_to_test,
+)
+def test_vertex_call_count_tokens(model_name: str) -> None:
+    llm = VertexAI(model_name=model_name)
     output = llm.get_num_tokens("How are you?")
     assert output == 4