Celestine Omin landed at New York's John F. Kennedy (JFK) airport on Feb. 26, on his way to work with technical recruitment and training firm Andela. But the Nigerian software engineer entered the United States at a time when foreign travelers have been placed under increased scrutiny, in large part thanks to President Donald Trump's emphasis on border security.

The 28-year-old was shocked when, according to an interview Omin gave to CNN, he was told by border officials that he didn't "look like an engineer" and was subsequently held for over three hours to prove his identity.

He was instructed that he needed to verify his computer science skills, and he was asked a series of complex questions, by U.S. Customers and Border Protection (CBP) officials who Omin claimed had no computer science training.

After what Omin described over Twitter as giving "Wikipedia definitions" to ten computer science questions, Omin was taken to another room. There he was given a blank sheet of paper and told to solve two extremely opaque and nuanced problems: “Write a function to check if a Binary Search Tree is balanced" and “what is an abstract class, and why do you need it?”

Having been traveling for an entire day, an exhausted Omin attempted to answer the questions, only to be told he was wrong by agents who Omin suspected had simply searched on Google to find software engineering questions and had no idea what they were actually looking at. Finally, after CBP officials spoke with a co-founder of Andela to corroborate Omin's identity, he was released to begin his work in the United States.

This isn't the first software engineer forced to verify his identity. Two weeks before Omin's interrogation, Australian programmer David Thornton landed at Newark International Airport in New Jersey to spend a week in the U.S. visiting family. But, first, he had a senior-level official ask him to take what Thornton described as "a literal computer science test."

While both Omin and Thornton were allowed into the U.S., the problem of engineers facing complex and poorly-administered vetting tests could have a profound effect on the American software industry.

In a LinkedIn post after the incident, Andela co-founder Jeremy Johnson described the urgent need for qualified engineers, as well as the growing foreign talent pool that can fill these jobs.

"[T]here are five job openings for every software developer looking for a job in the United States," Johnson wrote. "Africa, meanwhile, has the youngest, fastest-growing population on earth, with more people joining the labor force over the next 20 years than the rest of the world combined."

Johnson went on to write of the clash that Trump's "extreme vetting" will have on the effort to connect engineers with jobs, when these skilled and qualified workers come from countries with large Muslim populations, and little reputation for technical proficiency.

"America’s lack of technical talent will be the greatest challenge facing the tech industry over the next decade. [...] The best engineering firms realize that top talent can be found anywhere in the world, which is why more and more are moving toward a distributed model of work to hire the best people, regardless of location," he added. 

Johnson also told Linkedin that he fears Omin's experience is a sign of things to come, and that his firm will have a harder time recruiting and placing foreign engineers. He says the company followed up with Customs to clarify what happened, and what they can do to smooth the way for its engineers coming into the country but it hasn't heard back.

For its part, CPB gave a statement to CNN saying it doesn't "administer written tests to verify a traveler's purpose of travel."