tests: Add note about test suite naming convention

doc/developer-notes.md

@@ -34,6 +34,8 @@ code.
   - Constant names are all uppercase, and use `_` to separate words.
   - Class names, function names and method names are UpperCamelCase
     (PascalCase). Do not prefix class names with `C`.
+  - Test suite naming convention: The Boost test suite in file
+    `src/test/foo_tests.cpp` should be named `foo_tests`.
 
 - **Miscellaneous**
   - `++i` is preferred over `i++`.