# VTK leaks while testing
**URL:** https://discourse.slicer.org/t/vtk-leaks-while-testing/9026
**Category:** Development
**Tags:** vtk
**Created:** [November 5, 2019, 8:57am UTC](https://discourse.slicer.org/t/vtk-leaks-while-testing/9026 "2019-11-05T08:57:07Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Alex\_Vergara](https://discourse.slicer.org/u/Alex_Vergara)
#### Post date: [November 5, 2019, 8:57am UTC](https://discourse.slicer.org/t/vtk-leaks-while-testing/9026/1 "2019-11-05T08:57:07Z")
Basically I have this code for setting a default volume in the views
```python
mainWindow = slicer.util.mainWindow()
if mainWindow is not None:
layoutManager = slicer.app.layoutManager()
if layoutManager is not None:
sliceLogic = layoutManager.sliceWidget('Red').sliceLogic()
CompositeNode = sliceLogic.GetSliceCompositeNode()
CompositeNode.SetLinkedControl(1)
sliceLogic.StartSliceCompositeNodeInteraction(1)
CompositeNode.SetBackgroundVolumeID(minCTID)
CompositeNode.SetForegroundVolumeID(minSPECTID)
sliceLogic.EndSliceCompositeNodeInteraction()
layoutManager.setLayout(slicer.vtkMRMLLayoutNode.SlicerLayoutFourUpView)
slicer.util.resetSliceViews()
```
It works like a charm in normal mode, but when testing with `--no-main-window` it creates the following error
```bash
3: Test checkAttributes_positive passed!
3:
3: **************************************
3:
3: ok
3: runTest (slicer.ScriptedLoadableModule.ScriptedLoadableModuleTest) ... No test is defined in ScriptedLoadableModuleTest
3: ok
3:
3: ----------------------------------------------------------------------
3: Ran 2 tests in 0.732s
3:
3: OK
3: vtkDebugLeaks has detected LEAKS!
3: Class "vtkObserverManager" has 1 instance still around.
3: Class "vtkMRMLSliceCompositeNode" has 1 instance still around.
3: Class "vtkCommand or subclass" has 2 instances still around.
3:
3/4 Test #3: py_Dosimetry4DTest ...............***Failed 10.47 sec
```
As you can see the test passed, but the VTK leaks breaks the workflow
Without the above code, the VTK leaks are not present. However that code is not intended to run at all in no window mode, that is why I check if there is a main window. However, the check is failing as it creates the composite nodes. How is this possible?? Is there a way to NOT run a piece of code in no window mode??
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [November 5, 2019, 2:02pm UTC](https://discourse.slicer.org/t/vtk-leaks-while-testing/9026/2 "2019-11-05T14:02:59Z")
Have you included the complete test here? If there is no main window then the script above should not do anything.
---
### Author:  [@jamesobutler](https://discourse.slicer.org/u/jamesobutler)
#### Post date: [November 5, 2019, 2:44pm UTC](https://discourse.slicer.org/t/vtk-leaks-while-testing/9026/3 "2019-11-05T14:44:02Z")
I get the exact vtkDebugLeaks message only if I have implemented code in python such as `slicer.mrmlScene.CreateNodeByClass("vtkMRMLSliceCompositeNode")`.
See [https://www.slicer.org/wiki/Documentation/Nightly/Developers/Tutorials/MemoryManagement#Python\_scripts\_and\_scripted\_modules](https://www.slicer.org/wiki/Documentation/Nightly/Developers/Tutorials/MemoryManagement#Python_scripts_and_scripted_modules)
---
### Author:  [@Alex\_Vergara](https://discourse.slicer.org/u/Alex_Vergara)
#### Post date: [November 5, 2019, 2:48pm UTC](https://discourse.slicer.org/t/vtk-leaks-while-testing/9026/4 "2019-11-05T14:48:21Z")
@lassoan I found out that I was doing in the test
```python
def makeSlicerLinkedCompositeNodes():
# Set linked slice views in all existing slice composite nodes and in the default node
sliceCompositeNodes = slicer.util.getNodesByClass('vtkMRMLSliceCompositeNode')
defaultSliceCompositeNode = slicer.mrmlScene.GetDefaultNodeByClass('vtkMRMLSliceCompositeNode')
if not defaultSliceCompositeNode:
defaultSliceCompositeNode = slicer.mrmlScene.CreateNodeByClass('vtkMRMLSliceCompositeNode')
slicer.mrmlScene.AddDefaultNode(defaultSliceCompositeNode)
sliceCompositeNodes.append(defaultSliceCompositeNode)
for sliceCompositeNode in sliceCompositeNodes:
sliceCompositeNode.SetLinkedControl(True)
```
without checking properly if there was a Slicer window, this was the problem. So I changed the function to check for mainwindow first. Sorry for bothering you.