Add a function to decrypt a message with the gamma cipher.

test/cipher_analytical_machine/ciphers/gamma_test.clj

@@ -53,3 +53,10 @@
       [4 32 15] 33 [6 28 2 8 3 5 13 16 21 1] [3 14 1 4 18 19 23 8 27 17]
       [1 2  3 ] 3  [0 1 2 2 0 2 1 1 0]       [0 2 1 1 0 1 2 2 0])))
 
+(deftest decrypt-message-test
+  (testing "Checking that the message is decrypted as expected"
+    (are [key symbols message expected]
+        (= expected (decrypt-message key symbols message))
+      [4 32 15] "абвгґдеєжзиіїйклмнопрстуфхцчшщьюя" "ешвжгдймсб" "гкбґопужчн"
+      [1 2  3 ] "абв" "абввавбба" "авббабвва")))
+