Add string comparison tests.

Use computed string to exercise string interning code better.
diff --git a/tests/basics/tests/string1.py b/tests/basics/tests/string1.py
index 9d6f21d..3fecf79 100644
--- a/tests/basics/tests/string1.py
+++ b/tests/basics/tests/string1.py
@@ -10,3 +10,10 @@
 
 # iter
 print(list('str'))
+
+print('123' + '789' == '123789')
+print('a' + 'b' != 'a' + 'b ')
+
+# Not implemented so far
+# print('1' + '2' > '2')
+# print('1' + '2' < '2')