### Question
What is the definition of testing period?


### Answer
The definition of **testing period** is as follows in *26 U.S.C. § 861*:

> the 3-year period ending with the close of the taxable year of the individual or corporation preceding the payment (or such part of such period as may be applicable)

#### Citation:
  - *26 U.S.C. § 861*
  - Heading: **Subtitle A-Income Taxes > CHAPTER 1-NORMAL TAXES AND SURTAXES > Subchapter N-Tax Based on Income From Sources Within or Without the United States > PART I-SOURCE RULES AND OTHER GENERAL RULES RELATING TO FOREIGN INCOME**

