split node tests into standalone files

tests/node_tests/test_number.py

@@ -0,0 +1,10 @@
+def test_number():
+    from backend.nodes.number import Number
+
+    node = Number()
+
+    result = node.process(value=1.25)
+    assert result == (1.25,)
+
+    result_neg = node.process(value=-3.5)
+    assert result_neg == (-3.5,)