[tests] Fix broken test; see more

- Test preamble presence
- Transitions are written in unpredictable order => use a set
- Add doc

library/test/test_python_api.py

@@ -18,7 +18,8 @@ def feed_model_with_SCC():
     """
 
     scc = [['I', 'K', 'J', 'L'], ['Y', 'X', 'Z']]
-    model = """<model xmlns="http://cadbiom" name="">
+    model = """<?xml version = "1.0" encoding="ASCII" standalone="yes" ?>
+<model xmlns="http://cadbiom" name="">
   <CSimpleNode name="A" xloc="0.0" yloc="0.0"/>
   <CSimpleNode name="B" xloc="0.0" yloc="0.0"/>
   <CSimpleNode name="E" xloc="0.0" yloc="0.0"/>
@@ -57,7 +58,16 @@ def feed_model_with_SCC():
 
 
 def test_SCC_search(feed_model_with_SCC):
-    """
+    """Test the correction of a model by removing Strongly Connected Components
+
+    - We add a start node for every SCC
+    - We add a transition between the start node and the smallest node of every
+    SCC (sorted in lexicogrpahic order)
+
+    - Thus, we add xml preamble in the model
+
+    Keep in mind that by testing the result of the export of a model, we also
+    test its content...
     """
 
     import cadbiom.models.guard_transitions.analyser.model_corrections as mc
@@ -104,5 +114,8 @@ def test_SCC_search(feed_model_with_SCC):
     # Make a new model file (with "_without_scc" suffix in filename)
     mc.add_start_nodes(fd_model.name) # Filename + path
 
+    expected_lines = set(model.split("\n"))
+
     with open(fd_model.name[:-4] + "_without_scc.bcx", 'r') as file:
-        assert model == file.read()
+        found_lines = set(file.read().split("\n"))
+        assert found_lines == expected_lines