Add clear() method for Memory (#305)

a simple helper to clear the buffer in `Conversation*Memory` classes

tests/unit_tests/chains/test_conversation.py

@@ -4,6 +4,7 @@ import pytest
 from langchain.chains.base import Memory
 from langchain.chains.conversation.base import ConversationChain
 from langchain.chains.conversation.memory import (
+    ConversationalBufferWindowMemory,
     ConversationBufferMemory,
     ConversationSummaryMemory,
 )
@@ -66,3 +67,23 @@ def test_conversation_memory(memory: Memory) -> None:
     bad_outputs = {"foo": "bar", "foo1": "bar"}
     with pytest.raises(ValueError):
         memory.save_context(good_inputs, bad_outputs)
+
+
+@pytest.mark.parametrize(
+    "memory",
+    [
+        ConversationBufferMemory(memory_key="baz"),
+        ConversationSummaryMemory(llm=FakeLLM(), memory_key="baz"),
+        ConversationalBufferWindowMemory(memory_key="baz"),
+    ],
+)
+def test_clearing_conversation_memory(memory: Memory) -> None:
+    """Test clearing the conversation memory."""
+    # This is a good input because the input is not the same as baz.
+    good_inputs = {"foo": "bar", "baz": "foo"}
+    # This is a good output because these is one variable.
+    good_outputs = {"bar": "foo"}
+    memory.save_context(good_inputs, good_outputs)
+
+    memory.clear()
+    assert memory.load_memory_variables({}) == {"baz": ""}