Simple-Cipher: Validating Input Strings

Expand unit tests for validating input strings as per issue exercism#1298.
Three tests added covering:
- Keys containing a single upper case letter.
- Keys containing a space.
- Keys containing a punctuation mark.

Author: xarxziux

exercises/simple-cipher/canonical-data.json

@@ -87,7 +87,7 @@
           "expected": "qayaeaagaciai"
         },
         {
-          "description": "Can wrap on encode", 
+          "description": "Can wrap on encode",
           "property": "encode",
           "input": {
             "key": "abcdefghij",
@@ -126,6 +126,14 @@
           },
           "expected": { "error": "Bad key" }
         },
+        {
+          "description": "Throws an error with a key mixing upper and lower case letters",
+          "property": "new",
+          "input": {
+            "key": "abcdeFghij"
+          },
+          "expected": { "error": "Bad key" }
+        },
         {
           "description": "Throws an error with a numeric key",
           "property": "new",
@@ -134,6 +142,22 @@
           },
           "expected": { "error": "Bad key" }
         },
+        {
+          "description": "Throws an error with a key containg a space",
+          "property": "new",
+          "input": {
+            "key": "abcde fghij"
+          },
+          "expected": { "error": "Bad key" }
+        },
+        {
+          "description": "Throws an error with a key containing a punctuation mark",
+          "property": "new",
+          "input": {
+            "key": "abcde:fghij"
+          },
+          "expected": { "error": "Bad key" }
+        },
         {
           "description": "Throws an error with empty key",
           "property": "new",