You can take scores of tests on Embibe for free by selecting the exam (eg. JEE Main) and the type of test (eg. chapterwise test) you want to take as shown below:
In depth: Find out how to take tests on Embibe.
However, in order to get the feedback for each test, you have to unlock the Advanced Test Analysis by using Embiums or by buying them directly.
In depth: Read more about Embibe's Advanced Test Analysis here.