One of the officers then presented him with a piece of paper and a pen and told to answer these two questions to prove he is actually a software engineer:
"Write a function to check if a Binary Search Tree is balanced."
"What is an abstract class, and why do you need it?" [...]
After spending about 10 minutes working on them, he handed in his answers only to be told they were wrong.
As time passed, he said that he expected to be sent home to Nigeria, only for the official to let him go.
"He said, 'Look, I am going to let you go, but you don't look convincing to me,'" Omin said. "I didn't say anything back. I just walked out."
US immigration officials force Nigerian software engineer to complete written test to prove his computer knowledge
It looked to him like someone with no technical background Googled something like: 'Questions to ask a software engineer'