Having won the competition and the seed finance, for the next step why did they choose to specialise in what many would consider the dull world of testing?
As Kruustük tells it, she grew to like the whole process of software testing. She worked in London, among other places, and saw the flaws in the way testing was done.
"The more I got into testing, the more I realised that there was a huge variety in the way that companies do testing," she told ZDNet. "Some were thorough but many did not seem to do it properly or didn't know how to do it.
"It struck me that a lot of the testing being done wasn't very good. I could see that there were better ways to do it."
It appears to be working well for them. The company currently has a customer portfolio that is, "a touch over 650 million monthly users" and 60 employees in two offices, one in San Francisco, one in the Estonian capital of Tallinn.
Over the years, Testlio has developed a methodology for testing that aims to be thorough and flexible, enabling companies to implement the sort of methodology that suits them best. The company wants to be seen as a managed "testing-as-a-service" platform.
Testlio has around 200 testers, who between them work in 40 different countries, speaking 65 languages, and claims Microsoft, Salesforce, Lyft, Flipboard, Strava and GoDaddy among its customers.
Last April, Testlio raised a $6.25 million round of funding led by Altos Ventures and Vertex Ventures. According to the company, the funds will be invested in building out infrastructure across its two main locations.
One area the company has worked hard on is building a diverse workforce; the company workforce is 40 percent female. Kruustük points to a McKinsey report of 2015 -- Why Diversity Matters -- which showed there is a "statistically significant relationship between a more diverse leadership team and better financial performance".
It found that companies in the top quartile of gender diversity were 15 percent more likely to have financial returns that were above their national industry median - and for every 10 percent increase in racial and ethnic diversity on the senior-executive team," the report found, "earnings before interest and taxes (EBIT) rose 0.8 percent".
"That is exactly what we found," said Kruustük. "But our diversity doesn't just improve our bottom line; I think it makes working here a better experience for our employees, whatever their background."
In an article she contributed to Entrepreneur magazine, Kruustük said: "Over the long term, hiring a humble junior employee will almost always be a better decision than choosing someone more senior and less willing to learn".
Did that mean there is no place for older people at Testlio? Not at all, says Kruustük. "By seniority I meant their attitude and approach, especially if a person has been in the same role for a long time and has become inflexible in their ways.
"It's all about being open to new things and willing to learn -- whether you are 20 or 60 years old. And what I've found is people who are completely new to the role or industry are usually more open to learning new things, new approaches, getting out of their comfort zone, and bringing new ideas to the table."