test: add coverage for single tool_result and unexpected role paths

Add two tests to improve patch coverage:
- SingleToolResultNotCoalesced: verifies a single tool_result message
  (without consecutive ones) is handled correctly and not coalesced
  with a follow-up plain text user message.
- UnexpectedRole: verifies that an unexpected message role after system
  message promotion returns an error.

Signed-off-by: liuhy <liuhongyu@apache.org>

Author: Aias00

internal/translator/anthropic_awsbedrock_test.go

@@ -1181,6 +1181,116 @@ func TestAnthropicToAWSBedrockTranslator_RequestBody_ToolResultMessagesWithSyste
 	assert.Contains(t, *bedrockReq.System[0].Text, "Always be concise.")
 }
 
+func TestAnthropicToAWSBedrockTranslator_RequestBody_SingleToolResultNotCoalesced(t *testing.T) {
+	// Verify that a single tool_result message (without a consecutive one) is NOT coalesced
+	// but still goes through the tool result path (not convertUserMessage).
+	translator := NewAnthropicToAWSBedrockTranslator("")
+	req := &anthropicschema.MessagesRequest{
+		Model:     "test-model",
+		MaxTokens: 100,
+		Tools: []anthropicschema.ToolUnion{
+			{Tool: &anthropicschema.Tool{
+				Type:        "custom",
+				Name:        "get_weather",
+				Description: "Get weather",
+				InputSchema: anthropicschema.ToolInputSchema{Type: "object"},
+			}},
+		},
+		Messages: []anthropicschema.MessageParam{
+			{
+				Role:    anthropicschema.MessageRoleUser,
+				Content: anthropicschema.MessageContent{Text: "What's the weather?"},
+			},
+			{
+				Role: anthropicschema.MessageRoleAssistant,
+				Content: anthropicschema.MessageContent{
+					Array: []anthropicschema.ContentBlockParam{
+						{ToolUse: &anthropicschema.ToolUseBlockParam{
+							Type:  "tool_use",
+							ID:    "tu_abc",
+							Name:  "get_weather",
+							Input: map[string]any{"city": "NYC"},
+						}},
+					},
+				},
+			},
+			// Single tool result — no consecutive tool result to coalesce with.
+			{
+				Role: anthropicschema.MessageRoleUser,
+				Content: anthropicschema.MessageContent{
+					Array: []anthropicschema.ContentBlockParam{
+						{ToolResult: &anthropicschema.ToolResultBlockParam{
+							Type:      "tool_result",
+							ToolUseID: "tu_abc",
+							Content:   &anthropicschema.ToolResultContent{Text: "72°F and sunny"},
+						}},
+					},
+				},
+			},
+			// Follow-up user text message — should NOT be coalesced with tool result.
+			{
+				Role:    anthropicschema.MessageRoleUser,
+				Content: anthropicschema.MessageContent{Text: "Thanks!"},
+			},
+		},
+	}
+	rawBody, err := json.Marshal(req)
+	require.NoError(t, err)
+
+	_, body, err := translator.RequestBody(rawBody, req, false)
+	require.NoError(t, err)
+
+	var bedrockReq awsbedrock.ConverseInput
+	err = json.Unmarshal(body, &bedrockReq)
+	require.NoError(t, err)
+
+	// 4 messages: user, assistant, user(tool_result), user(text)
+	require.Len(t, bedrockReq.Messages, 4)
+
+	// Third message: tool result (not coalesced).
+	toolResultMsg := bedrockReq.Messages[2]
+	assert.Equal(t, awsbedrock.ConversationRoleUser, toolResultMsg.Role)
+	require.Len(t, toolResultMsg.Content, 1)
+	require.NotNil(t, toolResultMsg.Content[0].ToolResult)
+	assert.Equal(t, "tu_abc", *toolResultMsg.Content[0].ToolResult.ToolUseID)
+
+	// Fourth message: plain text (not coalesced with tool result).
+	textMsg := bedrockReq.Messages[3]
+	assert.Equal(t, awsbedrock.ConversationRoleUser, textMsg.Role)
+	require.Len(t, textMsg.Content, 1)
+	assert.NotNil(t, textMsg.Content[0].Text)
+	assert.Equal(t, "Thanks!", *textMsg.Content[0].Text)
+}
+
+func TestAnthropicToAWSBedrockTranslator_RequestBody_UnexpectedRole(t *testing.T) {
+	// Verify that an unexpected role returns an error.
+	translator := NewAnthropicToAWSBedrockTranslator("")
+	req := &anthropicschema.MessagesRequest{
+		Model:     "test-model",
+		MaxTokens: 100,
+		Messages: []anthropicschema.MessageParam{
+			{
+				Role:    anthropicschema.MessageRoleUser,
+				Content: anthropicschema.MessageContent{Text: "Hello"},
+			},
+			{
+				Role:    "system", // Will be promoted to system param.
+				Content: anthropicschema.MessageContent{Text: "You are helpful."},
+			},
+			{
+				Role:    "invalid_role",
+				Content: anthropicschema.MessageContent{Text: "This should fail"},
+			},
+		},
+	}
+	rawBody, err := json.Marshal(req)
+	require.NoError(t, err)
+
+	_, _, err = translator.RequestBody(rawBody, req, false)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "unexpected role: invalid_role")
+}
+
 func TestAnthropicToAWSBedrockTranslator_ResponseBody_NonStreamingToolUseAndReasoning(t *testing.T) {
 	translator := NewAnthropicToAWSBedrockTranslator("")
 	req := &anthropicschema.MessagesRequest{