This study aimed to answer an ongoing validity question related to the use of nonstandard English accents in international tests of English proficiency and associated issues of test fairness. More specifically, we examined (1) the extent to which different or shared English accents had an impact on listeners' performances on the Duolingo listening tests and (2) the extent to which different English accents affected listeners' performances on two different task types. Speakers from four interlanguage English accent varieties (Chinese, Spanish, Indian English [Hindi], and Korean) produced speech samples for "yes/no" vocabulary and dictation Duolingo listening tasks. Listeners who spoke with these same four English accents were then recruited to take the Duolingo listening test items. Results suggested that there is a shared first language (L1) benefit effect overall, with comparable test scores between shared-L1 and inner-circle L1 accents, and no significant differences in listeners' listening performance scores across highly intelligible accent varieties. No task type effect was found. The findings provide guidance to better understand fairness, equality, and practicality of designing and administering high-stakes English tests targeting a diversity of accents.