Add initial support for signal generators

test/test_signal_generator.py

@@ -50,6 +50,12 @@ def test_addition():
     assert g(2) == 2
     assert g(3) == 1
 
+    g = Impulse(1) + 1
+    assert g(0) == 1
+    assert g(1) == 2
+    assert g(2) == 1
+    assert g(3) == 1
+
 
 def test_subtraction():
     g = Impulse() - Impulse(2)
@@ -64,6 +70,12 @@ def test_subtraction():
     assert g(2) == 0
     assert g(3) == 1
 
+    g = Impulse(2) - 1
+    assert g(0) == -1
+    assert g(1) == -1
+    assert g(2) == 0
+    assert g(3) == -1
+
 
 def test_multiplication():
     g = Impulse() * 0.5