Add some graphID test fixtures

test/fixtures/graph_id.py

+import pytest
+from b_asic import GraphID, GraphIDGenerator
+
+"""
+Use a fixture for initializing objects and pass them as argument to a test function
+"""
+@pytest.fixture
+def graph_id():
+    return GraphID("add", 1)
+
+
+@pytest.fixture
+def graph_ids():
+    return [GraphID("add", 1), GraphID("add", 2), \
+        GraphID("sig", 1), GraphID("sig", 1), GraphID("sub", 3), \
+        GraphID("ÅÄÖ", 2), GraphID("", 3), \
+        GraphID("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 4)]
+    
+