Harrison/prompt template prefix (#888)

Co-authored-by: Gabriel Simmons <simmons.gabe@gmail.com>

tests/unit_tests/prompts/test_few_shot_with_templates.py

@@ -0,0 +1,40 @@
+"""Test few shot prompt template."""
+
+from langchain.prompts.few_shot_with_templates import FewShotPromptWithTemplates
+from langchain.prompts.prompt import PromptTemplate
+
+EXAMPLE_PROMPT = PromptTemplate(
+    input_variables=["question", "answer"], template="{question}: {answer}"
+)
+
+
+def test_prompttemplate_prefix_suffix() -> None:
+    """Test that few shot works when prefix and suffix are PromptTemplates."""
+    prefix = PromptTemplate(
+        input_variables=["content"], template="This is a test about {content}."
+    )
+    suffix = PromptTemplate(
+        input_variables=["new_content"],
+        template="Now you try to talk about {new_content}.",
+    )
+
+    examples = [
+        {"question": "foo", "answer": "bar"},
+        {"question": "baz", "answer": "foo"},
+    ]
+    prompt = FewShotPromptWithTemplates(
+        suffix=suffix,
+        prefix=prefix,
+        input_variables=["content", "new_content"],
+        examples=examples,
+        example_prompt=EXAMPLE_PROMPT,
+        example_separator="\n",
+    )
+    output = prompt.format(content="animals", new_content="party")
+    expected_output = (
+        "This is a test about animals.\n"
+        "foo: bar\n"
+        "baz: foo\n"
+        "Now you try to talk about party."
+    )
+    assert output == expected_output