Hi anjali,
So you mean like an editor that allows you to test the block-programs you write with blocks? I haven't heard of one, but that sounds really cool!
The closest things I can think of are:
1) MakeCode's
debugger interface, which allows you to set breakpoints and see variable state. Not related to unit testing, but debugging is kind of close to unit testing I hope? haha
2) Blockly's
generator tests. These are blocks that allow you to test that blockly's code generators are working correctly. You can't test your blockly /programs/, but it is unit testing!
Hopefully others have more resources for you!
--Beka