Add configuration to test connection strategy FixedOutdegree. (#5)

* Create additional file for outdegree connection test.

bsb_test/configs/outdegree.py

@@ -0,0 +1,34 @@
+required_plugins = []
+
+tree = {
+    "storage": {"engine": "fs"},
+    "network": {"x": 150.0, "y": 150.0, "z": 150.0},
+    "partitions": {"all": {"type": "layer", "thickness": 150.0}},
+    "cell_types": {
+        "inhibitory": {"spatial": {"radius": 1.0, "count": 2000}},
+        "excitatory": {"spatial": {"radius": 1.0, "count": 2000}},
+        "extra": {"spatial": {"radius": 1.0, "count": 2000}},
+    },
+    "placement": {
+        "random": {
+            "strategy": "bsb.placement.RandomPlacement",
+            "cell_types": ["inhibitory", "excitatory", "extra"],
+            "partitions": ["all"],
+        }
+    },
+    "connectivity": {
+        "outdegree": {
+            "strategy": "bsb.connectivity.FixedOutdegree",
+            "outdegree": 50,
+            "presynaptic": {"cell_types": ["excitatory"]},
+            "postsynaptic": {"cell_types": ["inhibitory"]},
+        },
+        "multi_outdegree": {
+            "strategy": "bsb.connectivity.FixedOutdegree",
+            "outdegree": 50,
+            "presynaptic": {"cell_types": ["excitatory", "extra"]},
+            "postsynaptic": {"cell_types": ["inhibitory", "extra"]},
+        },
+    },
+    "simulations": {},
+}