### Question
How is the "testing period" defined?


### Answer
The term **testing period** is defined in *26 U.S.C. § 871* as follows -

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

#### Citation:
  - *26 U.S.C. § 871*
  - 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 II-NONRESIDENT ALIENS AND FOREIGN CORPORATIONS > Subpart A-Nonresident Alien Individuals**

