Doctors Alfred Kinsey, Wardell Pomeroy, and Clyde Marten developed "The Kinsey Scale" (sometimes known as the Heterosexual-Homosexual Rating Scale) in 1948, because research was finding people did not fit into exclusive homo or hetero categories.
The Kinsey Scale uses a seven-point scale, ranging from 0 (exclusively heterosexual) to 6 (exclusively homosexual) with an additional category of "X" which is the sort of "asexual" category.
Ratings 0 and 6 are for those who consider themselves exclusively heterosexual or homosexual, with no experience with or desire for sexual activity with the same sex, or opposite sex respectively.
So ratings 1-5 are a big bisexual umbrella for those who are not exclusively hetero or homosexual, and rather have varying levels of desire for sexual activity with either sex.
There is no official "Kinsey Scale Test", although there are many tests available online that will plot you somewhere on the scale. However I tried 3 today and each gave me a different score.
The Kinsey Scale of course does not address all possible sexual identities, and in the time since it's first publication there have been hundreds of attempts at other scales or tests to better measure and describe sexual orientation.