fix GetUploadURLExternalContext error message

Author: YutoKashiwagi

files.go

@@ -510,10 +510,10 @@ func (api *Client) ShareFilePublicURLContext(ctx context.Context, fileID string)
 // Slack API docs: https://api.slack.com/methods/files.getUploadURLExternal
 func (api *Client) GetUploadURLExternalContext(ctx context.Context, params GetUploadURLExternalParameters) (*GetUploadURLExternalResponse, error) {
 	if params.FileName == "" {
-		return nil, fmt.Errorf("GetUploadURLExternalContext: fileName cannot be empty")
+		return nil, fmt.Errorf("files.getUploadURLExternal: fileName cannot be empty")
 	}
 	if params.FileSize == 0 {
-		return nil, fmt.Errorf("GetUploadURLExternalContext: fileSize cannot be 0")
+		return nil, fmt.Errorf("files.getUploadURLExternal: fileSize cannot be 0")
 	}
 
 	values := url.Values{

files_test.go

@@ -357,15 +357,15 @@ func TestGetUploadURLExternalContext(t *testing.T) {
 				FileName: "",
 				FileSize: 10,
 			},
-			wantErr: fmt.Errorf("GetUploadURLExternalContext: fileName cannot be empty"),
+			wantErr: fmt.Errorf("files.getUploadURLExternal: fileName cannot be empty"),
 		},
 		{
 			title: "Testing with invalid parameters: file size 0",
 			params: GetUploadURLExternalParameters{
 				FileName: "test.txt",
 				FileSize: 0,
 			},
-			wantErr: fmt.Errorf("GetUploadURLExternalContext: fileSize cannot be 0"),
+			wantErr: fmt.Errorf("files.getUploadURLExternal: fileSize cannot be 0"),
 		},
 	}