I came across the following sentence, but I'm not sure that it's correct:
From what of the product we could test, there are still some problems.
Could you please tell me if it's a correct form? Thank you!
This form is not idiomatic in its expression. The idea is that:
There are three main errors in this statement.
First, 'what' implies certainty. If you say 'I want to do what I love', it implies that you already have a notion of what it is you love and that you want to do just that. This is different to saying 'I want to do something I love', because 'something' implies a lack of certainty - that you are open to possibilities and that you are not fixated on one thing. In the statement, it is unclear how 'what' is used; it may imply that the components tested were not defined or it may imply that they were defined.
Second, 'what of' modifies 'product'. If you want to refer to a subset of something bigger, it is better to use a definite noun, e.g. 'elements of the product', 'components of the product', 'bits of the product' etc., instead of 'what of the product'. This is more idiomatic.
Third, the sentence is saying that, when the product was tested, problems were observed. One cannot say '...there are problems' (meaning problems are currently present) simultaneously with '..product we could test' (meaning the testing took place in the past), because presumably, problems were observed during the testing, and if so, both clauses should be in the past tense.
Better statements could be:
We found problems in the product elements that we were able to test
We found problems in the product components that we tested
If you now wanted to say that these problems are still present, then this should be done as a separate statement. E.g.
We found problems in the product components that we tested. These problems are still present in our product.
Those three words in a row (From what of) are idiomatically unusual. And though I've no doubt someone will argue that the sentence is grammatical, if it is not readily understood, what good is that?
My way of saying it might be:
From as much of the product as we could test, there are still problems.
Of course that does not necessarily mean the same thing. The constraining factor may not have been the quantity but the particular elements submitted for test. In which case a modification may be needed:
From those elements of the product we could test, there are still problems.