Literacy tests were introduced into the voting process in the South with the Jim Crow laws. Jim Crow laws were state and local laws and statutes enacted by southern and border states in the late 1870s to deny Blacks the right to vote in the South following Reconstruction (1865-1877).
Despite the ratification of the 14th Amendment in 1868, granting citizenship to "all persons born or naturalized in the United States" which included former slaves, and the ratification of the 15th Amendment in 1870, which specifically gave Blacks the right to vote, Southern and Border states continued to find ways to keep racial minorities from voting. They used electoral fraud and violence to intimidate Blacks voters, and created Jim Crow laws to promote racial segregation.
Below are scans of the actual "literacy test" given to black voters by the state of Louisiana in the 1960s.The test was to be taken in 10 minutes flat, and a single wrong answer meant a failing grade. Besure to note the irony of the typos in this test.