Add test for subsystem

Author: Flamefire

test/test_subsystem.py

@@ -0,0 +1,20 @@
+import os
+from scorep import subsystem
+
+
+def test_reset_preload(monkeypatch):
+    monkeypatch.setenv('LD_PRELOAD', '/some/value')
+    # Nothing changes if the var is not present
+    monkeypatch.delenv('SCOREP_LD_PRELOAD_BACKUP', raising=False)
+    subsystem.reset_preload()
+    assert os.environ['LD_PRELOAD'] == '/some/value'
+
+    # Variable set -> Update
+    monkeypatch.setenv('SCOREP_LD_PRELOAD_BACKUP', '/new/value')
+    subsystem.reset_preload()
+    assert os.environ['LD_PRELOAD'] == '/new/value'
+
+    # Variable empty -> remove
+    monkeypatch.setenv('SCOREP_LD_PRELOAD_BACKUP', '')
+    subsystem.reset_preload()
+    assert 'LD_PRELOAD' not in os.environ