Fix execute_command coming from plugins (#4730)

tests/unit/test_execute_command.py

@@ -0,0 +1,24 @@
+from autogpt.agent import Agent
+from autogpt.app import execute_command
+
+
+def check_plan():
+    return "hi"
+
+
+def test_execute_command_plugin(agent: Agent):
+    """Test that executing a command that came from a plugin works as expected"""
+    agent.ai_config.prompt_generator.add_command(
+        "check_plan",
+        "Read the plan.md with the next goals to achieve",
+        {},
+        check_plan,
+    )
+    command_name = "check_plan"
+    arguments = {}
+    command_result = execute_command(
+        command_name=command_name,
+        arguments=arguments,
+        agent=agent,
+    )
+    assert command_result == "hi"