Add tests to check assignment works with tuple unpacking.

tests/snippets/assignment.py

@@ -0,0 +1,28 @@
+x = 1
+assert x == 1
+
+x = 1, 2, 3
+assert x == (1, 2, 3)
+
+x, y = 1, 2
+assert x == 1
+assert y == 2
+
+x, y = (y, x)
+
+assert x == 2
+assert y == 1
+
+((x, y), z) = ((1, 2), 3)
+
+assert (x, y, z) == (1, 2, 3)
+
+q = (1, 2, 3)
+(x, y, z) = q
+assert y == q[1]
+
+x = (a, b, c) = y = q
+
+assert (a, b, c) == q
+assert x == q
+assert y == q