We're about to launch our MVP and as the sole designer of the team, I know we will have some usability issues. Besides, I want to know if the product is a market fit because the main members of the team didn't conduct proper user research, only some small market research. Therefore, I want to conduct Interviews with users and then do Usability testing for onboarding process. Do you think this would be possible? Thanks.
Possible? Yes, it is possible.
Useful? Perhaps, but quite unlikely.
In terms of methodology, it is not recommended because there will be cognitive loads and biases that will affect the outcome.
But more importantly, whatever results you get will not matter.
The thing is that, as you say, the original research was not done properly. Therefore, the result of your usability tests will have no impact on the feasibility of the product. I mean: Let us say the results of your usability tests are great. Would it matter if the product or service is a poor fit for the market?
What to do? If it is within your capabilities, I would suggest that you talk to your team and start researching the product itself.
Otherwise, just focus on the usability and try to do the best you can, maybe the product will be a market fit anyway, so make sure the usability is as good as possible
Assuming that you want to do Qualitative Usability testing - you can do it, but if you want to follow standard there totally then users in usability testing should not have any emotional connection with the brand or be affected in any other case before they start it(you should not evoke any emotions or discover them things during Interview before testing).
You will probably get precise enough results to draw conclusion, but you should take exact numbers, depending on what you are measuring - with a "grain of salt".
I think it would lead to faulty results.
First of all, you should do exploring interviews, then a usability test, and then an acceptance test, but each separately.
Exploring interviews is good to build up your domain knowledge and to better understand user needs > and most of all, it helps you create user/job stories.
During usability tests we ALWAYS test hypotheses. These hypotheses were formed by processing the results of previous studies. (Exploring interviews, best practice research, etc.)
Acceptance tests are about finding out, whether your solution will meet your audience/customer needs or not. The main difference from a usability test is that during an acceptance test we show everything and describe how it works, so users can have feedback about it. (More detailed way than during the usability test.) During a usability test, you are testing how your design works. During an acceptance test, you are getting feedback that your solution is good enough for your customer or not. (An usability test can be successful, and still a wrong solution)
So, merging these tests is not a good idea, because they are followed each other, but what connects them, is the processed data/findings.
From my perspective and explerience you cannot do both at the sametime. The user interview is done in the beginning of the product design to collect users painpoints and to find answer or solution to those frustration which lies in the gap between the present and the future product designs. Then design and prototype the designs. It is only at this evaluation stage that you conduct the usability tests by assigning a task or tasks to users to complete to see and understand the effectiveness and efficiency of the designs also memorability and satisfaction.
Yes, you can ask users or interview them about the usability test releted questions without providing any cues to the conduct of the test. However, I do not think one can do an exploratory user research interview at this point of time.