how should we code for testing the stegnography programe.. please help me..!!

The testing methods are pretty simple, at least to start with:
1) Set up a set of images, and sample files to "hide"
2) Loop though each image, and "hide" each sample file in it, saving them to new image files.
3) Then loop through each of the saved image files, and "extract" the hidden data. Compare it to the files your hid in the first place.

If you can successfully match each file, byte-for-byte from each image, then you have a reasonable idea that the code works. If not, then back to development with you!

If they are fine, then you need to look at the output files visually and see if you can detect any "tampering" if you can't, then you're probably there.

It's worth using a range of images, in various sizes, and a range of inputs of different types - including all nulls, and all 0xFF bytes, as well as binary and text based data.