What were civil service examinations and why were they created?

In the United States many governmental positions are not by political appointment but instead candidates are chosen based on the results of Civil Service Examination Tests.

The two fold purpose in this is to avoid "political " appointments and to have candidates for civil service be knowledgeable enough to serve in various positions.

An example of this is a test given by the Federal Government to select Internal Revenue Agents. Its an all day test and the scores of the candidates are part of the selection process.