Merge pull request #155 from aciidb0mb3r/patch-1

Update SourceLayouts.md - Tests directory

Author: mxcl

Documentation/SourceLayouts.md

@@ -35,6 +35,6 @@ Where `foo` is an executable and `bar.a` a static library.
 
 ## Other Rules
 
-* Directories named `Tests` are ignored
-* Sub directories of a directory named `Sources`, `Source`, `srcs` or `src` become modules
+* Sub directories of directory named `Tests` become test-modules and are executed by `swift test`. `Tests` or any subdirectory can be excluded via Manifest file.
+* Sub directories of a directory named `Sources`, `Source`, `srcs` or `src` become modules.
 * It is acceptable to have no `Sources` directory, in which case the root directory is treated as a single module (place your sources there) or sub directories of the root are considered modules. Use this layout convention for simple projects.