Updated coding standard to explain unit testing

Moved the sharing map test into the appropriate folder

CODING_STANDARD

@@ -171,6 +171,23 @@ Output:
   (status(), error(), debug(), etc)
 - Use '\n' instead of std::endl
 
+Unit tests:
+ - Unit tests are written using Catch: https://github.com/philsquared/Catch/
+ - For large classes:
+    - Create a separate file that contains the tests for each method of each
+      class
+    - The file should be put inside unit/class/path/class_name/function_name.cpp
+ - For small classes:
+    - Create a separate file that contains the tests for all methods of each
+      class
+    - The file should be put inside unit/class/path/class_name.cpp
+ - Catch supports tagging, tests should be tagged with:
+    - [core] should be used for all tests unless the test takes more than 1
+      second to run, then it should be tagged with [long]
+    - [folder_name] of the file being tested
+    - [class_name] of the class being tested
+    - [function_name] of the function being tested
+
 You are allowed to break rules if you have a good reason to do so.
 
 Pre-commit hook to run cpplint locally