Fix flaky ObjectClassificationGui test (ilastik#2911)

this test was flaky due to so many features in training - fixing the
seed for the RF training should fix this.

In the test class the following comparisons against of exported data
to reference data would fail occasionally.

Also removed some unused imports.

tests/conftest.py

@@ -1,11 +1,8 @@
 from pathlib import Path
 import os
-import shutil
 import tempfile
 import threading
-import time
 import queue
-import sys
 import warnings
 import platform
 import itertools
@@ -358,3 +355,24 @@ def cacheMemoryManager(monkeypatch):
     mem_manager = _CacheMemoryManager()
     monkeypatch.setattr(lazyflow.operators.cacheMemoryManager, "_cache_memory_manager", mem_manager)
     return mem_manager
+
+
+@pytest.fixture()
+def reliable_vigra_train_rf_seed(monkeypatch):
+    """
+    Can be used in test functions that involve invoking
+    `vigra.learning.RandomForest.learnRF` along the way. This will set
+    the randomSeed parameter in that function to 42.
+    Relies on `learnRF` being called only with parameters trainData and trainLabels.
+    """
+    import vigra
+
+    _learn_orig = vigra.learning.RandomForest.learnRF
+    randomSeed = 42
+
+    # Note: can't use a partial there, the function doesn't like kwargs
+    monkeypatch.setattr(
+        vigra.learning.RandomForest,
+        "learnRF",
+        lambda self, trainData, trainLabels: _learn_orig(self, trainData, trainLabels, randomSeed),
+    )

tests/test_ilastik/test_workflows/testObjectClassificationGui.py

@@ -31,6 +31,7 @@
 
 import h5py
 import numpy
+import pytest
 
 from ilastik.workflows import ObjectClassificationWorkflowPrediction
 from ilastik.applets.dataSelection.opDataSelection import FilesystemDatasetInfo
@@ -364,6 +365,7 @@ def impl():
         # Run this test from within the shell event loop
         self.exec_in_shell(impl)
 
+    @pytest.mark.usefixtures("reliable_vigra_train_rf_seed")
     def test_05_live_update_mode(self):
         def impl():
             shell = self.shell