elaborate test runnin

Assignments.md

@@ -10,6 +10,10 @@ build, run and test it. The testing process is divided into stages.
 
 ### Tests
 
+A test is a pair of files, where the first one specifies an input and the other 
+one the expected output. Tests can be organized into groups for easier 
+organization and to facilitate more complex grading scenarios (e.g. "An 
+assignment passes only if it passes all tests in group X").
 
 ### Stages
 
@@ -20,8 +24,12 @@ contained in its configuration:
 - **Name** - a unique string identifier of the stage
 - **Build command** (optional) - used to prepare the submitted files for this 
   test stage
-- **Test list** - specifies the tests to be run during this stage
+- **Test list** - specifies the tests (or test groups) to be run during this 
+  stage
 - **Test command** - used to run one specific test
+- **Test input policy** - how to pass the test input to the program?
+	- redirect it to its standard input
+	- pass the name of the input file as an argument
 - **Error policy** (optional) - what should we do when a test fails?
 	- **interrupt** the stage (default)
 	- **continue** with the next test