diff --git a/src/cipher_analytical_machine/caesar_analyzers.clj b/src/cipher_analytical_machine/caesar_analyzers.clj
index 841dd17..4d71f06 100644
--- a/src/cipher_analytical_machine/caesar_analyzers.clj
+++ b/src/cipher_analytical_machine/caesar_analyzers.clj
@@ -1,5 +1,6 @@
 (ns cipher-analytical-machine.caesar-analyzers
   (:require [cipher-analytical-machine.caesar :as caesar]
+            [clojure.string :as cs]
             [cipher-analytical-machine.cipher-analyzers :as ca])
   (:gen-class))
 
@@ -12,23 +13,36 @@
        (conj acc [key (caesar/decrypt-message ciphertext key symbols)]))
      '() keys)))
 
+(defn get-all-scores
+  "For pairs (key, plaintext) finds scores and return list of pairs [key, score]."
+  [letter-frequences pairs]
+  (map (fn [[key text]]
+         [key (ca/chi-squared-statistic text letter-frequences)])
+       pairs))
+
+(defn get-min-score-pair
+  "For pairs (key, plaintext) finds scores and return list of pairs [key, score]."
+  [pairs]
+  (reduce
+   (fn [[key value] [new-key new-value]]
+     (if (> value new-value) [new-key new-value]
+         [key value]))
+   [0 Double/MAX_VALUE]
+   pairs))
+
 (defn get-key
   "To find the key with frequencies of letters."
   [ciphertext symbols letter-frequences]
   (->> (get-all-texts ciphertext symbols)
-       (map (fn [[key text]]
-              [key (ca/chi-squared-statistic text letter-frequences)]))
-       (reduce
-        (fn [[key value] [new-key new-value]]
-          (if (> value new-value) [new-key new-value]
-               [key value]))
-        [0 Double/MAX_VALUE])
+       (get-all-scores letter-frequences)
+       (get-min-score-pair)
        (first)))
 
 (defn get-plaintext
-  "Return the plaintext from a ciphertext."
+  "Return the plaintext from a ciphertext. The function is case-insensitive."
   [ciphertext symbols letter-frequences]
-  (caesar/decrypt-message ciphertext
-                          (get-key ciphertext symbols letter-frequences)
-                          symbols))
+  (let [ciphertext (cs/lower-case ciphertext)]
+    (caesar/decrypt-message ciphertext
+                            (get-key ciphertext symbols letter-frequences)
+                            symbols)))
 
diff --git a/test/cipher_analytical_machine/caesar_analyzers_test.clj b/test/cipher_analytical_machine/caesar_analyzers_test.clj
new file mode 100644
index 0000000..2a06d97
--- /dev/null
+++ b/test/cipher_analytical_machine/caesar_analyzers_test.clj
@@ -0,0 +1,76 @@
+(ns cipher-analytical-machine.caesar-analyzers-test
+  (:require
+   [clojure.test :refer :all]
+   [cipher-analytical-machine.caesar-analyzers :refer :all]
+   [cipher-analytical-machine.symbol-frequences :as sf]
+   [cipher-analytical-machine.cipher-analyzers :as ca]
+   [clojure.string :as cs]))
+
+(deftest get-all-texts-test
+  (testing "There're three text when the text is 'abc' and the set of symbol is 'abc'."
+    (is (= 3 (count (get-all-texts "abc" "abc")))))
+
+  (testing "A pair must have an integer and a string."
+    (let [pairs (get-all-texts "abc" "abc")
+          pair (first pairs)]
+      (is (and (int? (first pair))
+               (string? (last pair))))))
+
+  (testing "There're 27 combinations for a 'Hello World'."
+    (let [ciphertext "khoorczruog"
+        symbols "abcdefghijklmnopqrstuvwxyz "]
+      (is (= 27 (count (get-all-texts ciphertext symbols)))))))
+
+(deftest get-all-scores-test
+  (testing "There're 27 combinations for a 'Hello World'."
+    (let [ciphertext "khoorczruog"
+          symbols "abcdefghijklmnopqrstuvwxyz "
+          frequences sf/english-letter-frequences
+          text-pairs (get-all-texts ciphertext symbols)]
+      (is (= 27 (count (get-all-scores frequences text-pairs)))))))
+
+(deftest get-min-score-pair-test
+  (testing "If a key is one, then the min score pair is 15."
+    (let [scores (list [0 20.0] [1 15.0] [2 30.0])
+          min-score-pair (get-min-score-pair scores)]
+      (is (= [1 15.0] min-score-pair)))))
+
+(deftest get-key-test
+  (let [plaintext "hello world"
+        ciphertext "khoorczruog"
+        key 3
+        symbols "abcdefghijklmnopqrstuvwxyz "
+        frequences sf/english-letter-frequences]
+    (testing "The plaintext is encrypted with 3 as the key."
+      (is (= key (get-key ciphertext symbols frequences)))))
+
+  (let [; З поеми "Кавказ" Тараса Григоровича Шевченка:
+        plaintext "Борітеся – поборете, Вам Бог помагає! За вас правда, за вас слава. І воля святая!"
+        ciphertext "жхчощйшде–ецхжхчйщй,езєуежхиецхуєиєк!емєезєшецчєзїє,емєезєшештєзє.еоезхтдешздщєд!"
+        key 7
+        symbols "абвгґдеєжзиіїйклмнопрстуфхцчшщьюя "
+        frequences sf/ukrainian-letter-frequences]
+    (testing "The plaintext is encrypted with 3 as the key."
+      (is (= key (get-key ciphertext symbols frequences))))))
+
+(deftest get-plaintext-test
+  (let [plaintext "hello world"
+        ciphertext "khoorczruog"
+        symbols "abcdefghijklmnopqrstuvwxyz "
+        frequences sf/english-letter-frequences]
+    (testing "The plaintext is encrypted with 3 as the key."
+      (is (= plaintext (get-plaintext ciphertext symbols frequences))))
+
+    (testing "The ciphertext is case-insensitive."
+      (is (= plaintext (get-plaintext "KhoorcZruog" symbols frequences)))))
+
+  (let [; З поеми "Кавказ" Тараса Григоровича Шевченка:
+        plaintext "Борітеся – поборете, Вам Бог помагає! За вас правда, за вас слава. І воля святая!"
+        ciphertext "жхчощйшде–ецхжхчйщй,езєуежхиецхуєиєк!емєезєшецчєзїє,емєезєшештєзє.еоезхтдешздщєд!"
+        key 7
+        symbols "абвгґдеєжзиіїйклмнопрстуфхцчшщьюя "
+        frequences sf/ukrainian-letter-frequences]
+    (testing "The ciphertext is case-insensitive."
+      (is (= (cs/lower-case plaintext)
+             (get-plaintext ciphertext symbols frequences))))))
+