Here is Googles eligibility test :

A Bachelors degree in Engineering with a good academic record .
Good knowledge in internet , web-search, online advertising , numerical analysis ,fraud detection and e-commerce .
Good written, verbal and interpersonal communication skills and ability to communicate clearly and efficiently .
There are various sections included in the test during test conduction . Various sectionsare :
Questions from computer awareness
Verbal reasoning
Quantitative aptitude
Critical reasoning
And the standard of the questions depends upon the nature of the post .
The candidates who clear the written test are further called up for the interview .
There is a psychometric test , which is conducted to identify the personality, behaviour ,social activities , qualities and values of the candidates. Candidate who is selected after the psychometric test will be then called for a technical interview.

After technical interview , there will be HR interview which includes some personal questions.

Good Luck!