What is Test cases?Example of Test cases?

A document which describe input action or event and expected response to determine the future of  an application is working correctly .
it should contain particulars such as 
test case Identifier,
test case name ,
objectives , 
test conditions input data requirements ,
steps and expected results .

Test Case:	TC-UC-40 Customize the application look and feel
Description:	Allow users to configure their view of the system by customizing an existing template.  Upon completion, the application is updated to reflect the new configuration.
Primary Actors:	User	Executed By:
Preconditions:	User is logged in	Date Executed:
Success Guarantees:		Version/Build #:
Setup:	Start application from start menu, log in as Guest (pw: Guest).  Open MySampleDoc found in Samples folder.
Configurations:	XP, IE6, .Net 1.1 or .Net 2.0 Win2K, IE5.5, .Net 1.1 XP, IE6, French, .Net 1.1

TC-UC-40-Main	Procedure / Inputs	Expected Results	Pass/Fail
1.  User chooses to configure their view	Access from: tools menu, via F6, via toolbar	Configuration dialog appears
2.  System presents a list of templates		List should be sortable by name or date
3.  User selects a template to configure	Try each standard template, but also browse to other non-standard templates: - Empty template - Version 1.0 template
4.  System enters edit mode		Editor dialog shows contents of template in modal window.  Default values (from system config file) should be used for values that aren't specified in the template.
5.  User changes, adds and deletes appearance properties	Try combinations of: - Point size: 10, 12, 14 - Background: image.bmp, solid - Font face: Arial, Courier
6.  User saves changes and exits	Select "Apply" button, then select OK.	Original template is not overwritten (verify by checking date of template file)
7.  System updates view to reflect user's modifications		Values from new template plus user's changes within the template are used.

TC-UC-40-1	Procedure / Inputs	Expected Results	Pass/Fail
3.a  Template file is missing	Delete or rename template file found in \program files\...\shared\templates

1.  System informs user that template is unavailable		Standard error dialog
2.  continue at step 2

TC-UC-40-2	Procedure / Inputs	Expected Results	Pass/Fail
3.b  User doesn't have adequate permissions to modify template	Login as user that doesn't have admin rights

1.  System informs user that template is protected		Warning dialog
2.  continue at step 2

TC-UC-40-3	Procedure / Inputs	Expected Results	Pass/Fail
5.a  User performs an illegal action	- Select point size greater than 24 - Enter missing image file - Erase font face

1.  System notifies user of error and its cause

Shows line number of where error occurred

TC-UC-40-4	Procedure / Inputs	Expected Results	Pass/Fail
6.a  User exits without saving changes	Don't select Apply, select OK

1.  System verifies that is what the user wants to do

Answer yes

Nothing changes in the view

Requirements		Procedure / Inputs	Pass/Fail
REQ-20	Help must be available	If on a form, verify help button exists and functions. Verify F1 works in all situations.
REQ-21	Feature must be available offline	Unplug network connection.  Test main success scenario.
REQ-4-1	Dialog must display in 2 seconds or less	Turn on built-in timer by starting app with -t switch.  Examine log results in c:\timer.log