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


### Answer
The term **testing period** is defined in *26 U.S.C. § 6655* as follows -

> the 3 taxable years immediately preceding the taxable year involved

#### Citation:
  - *26 U.S.C. § 6655*
  - Heading: **Subtitle F-Procedure and Administration > CHAPTER 68-ADDITIONS TO THE TAX, ADDITIONAL AMOUNTS, AND ASSESSABLE PENALTIES > Subchapter A-Additions to the Tax and Additional Amounts > PART I-GENERAL PROVISIONS**

