style: align prompt test structure with tools test convention

Wrap test functions in TestPrompts class and move imports to
module level, matching the pattern used in tests/tools/.

Author: paikend

tests/prompts/test_prompts.py

@@ -1,29 +1,31 @@
-from openstack_mcp_server.prompts import register_prompt
+from unittest.mock import MagicMock
 
+from fastmcp import FastMCP
 
-def test_get_servers_by_security_group_prompt_registered():
-    """Test that the prompt is registered with the MCP instance."""
-    from unittest.mock import MagicMock
+from openstack_mcp_server.prompts import register_prompt
 
-    mcp = MagicMock()
-    register_prompt(mcp)
-    mcp.prompt.assert_called()
 
+class TestPrompts:
+    """Test cases for MCP prompts."""
 
-def test_get_servers_by_security_group_prompt_content():
-    """Test that the prompt returns expected content."""
-    from fastmcp import FastMCP
+    def test_get_servers_by_security_group_prompt_registered(self):
+        """Test that the prompt is registered with the MCP instance."""
+        mcp = MagicMock()
+        register_prompt(mcp)
+        mcp.prompt.assert_called()
 
-    mcp = FastMCP("test")
-    register_prompt(mcp)
+    def test_get_servers_by_security_group_prompt_content(self):
+        """Test that the prompt returns expected content."""
+        mcp = FastMCP("test")
+        register_prompt(mcp)
 
-    prompts = mcp._prompt_manager._prompts
-    assert "get_servers_by_security_group" in prompts
+        prompts = mcp._prompt_manager._prompts
+        assert "get_servers_by_security_group" in prompts
 
-    prompt_obj = prompts["get_servers_by_security_group"]
-    assert prompt_obj.fn is not None
+        prompt_obj = prompts["get_servers_by_security_group"]
+        assert prompt_obj.fn is not None
 
-    result = prompt_obj.fn(security_group_name="my-sg")
-    assert "my-sg" in result
-    assert "get_servers" in result
-    assert "security_groups" in result
+        result = prompt_obj.fn(security_group_name="my-sg")
+        assert "my-sg" in result
+        assert "get_servers" in result
+        assert "security_groups" in result