test(cast): add new test for dropping multiple nil function call tool calls

- Introduced a new test case to verify that multiple nil FunctionCall tool calls are correctly removed from the message content, ensuring only relevant text parts are retained.
- Removed the previous test file `newbodypair_reg_test.go` as its functionality is now covered in the updated test suite.

backend/pkg/cast/chain_ast_test.go

@@ -3213,3 +3213,23 @@ func TestSanitizeToolCallArguments(t *testing.T) {
 		})
 	}
 }
+
+func TestNewBodyPair_DropsMultipleNilFunctionCallToolCalls(t *testing.T) {
+	aiMsg := &llms.MessageContent{
+		Role: llms.ChatMessageTypeAI,
+		Parts: []llms.ContentPart{
+			llms.ToolCall{ID: "a", Type: "function", FunctionCall: nil},
+			llms.ToolCall{ID: "b", Type: "function", FunctionCall: nil},
+			llms.TextContent{Text: "keep me"},
+		},
+	}
+
+	NewBodyPair(aiMsg, nil)
+
+	assert.Len(t, aiMsg.Parts, 1, "both nil-FunctionCall tool calls should be removed, text kept")
+	if assert.Len(t, aiMsg.Parts, 1) {
+		txt, ok := aiMsg.Parts[0].(llms.TextContent)
+		assert.True(t, ok, "surviving part should be the TextContent, got %T", aiMsg.Parts[0])
+		assert.Equal(t, "keep me", txt.Text)
+	}
+}

backend/pkg/cast/newbodypair_reg_test.go

@@ -1,28 +0,0 @@
-package cast
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/vxcontrol/langchaingo/llms"
-)
-
-func TestNewBodyPair_DropsMultipleNilFunctionCallToolCalls(t *testing.T) {
-	aiMsg := &llms.MessageContent{
-		Role: llms.ChatMessageTypeAI,
-		Parts: []llms.ContentPart{
-			llms.ToolCall{ID: "a", Type: "function", FunctionCall: nil},
-			llms.ToolCall{ID: "b", Type: "function", FunctionCall: nil},
-			llms.TextContent{Text: "keep me"},
-		},
-	}
-
-	NewBodyPair(aiMsg, nil)
-
-	assert.Len(t, aiMsg.Parts, 1, "both nil-FunctionCall tool calls should be removed, text kept")
-	if assert.Len(t, aiMsg.Parts, 1) {
-		txt, ok := aiMsg.Parts[0].(llms.TextContent)
-		assert.True(t, ok, "surviving part should be the TextContent, got %T", aiMsg.Parts[0])
-		assert.Equal(t, "keep me", txt.Text)
-	}
-}