Questions & Answers about Uusi funktio on mukava testata.
Why is mukava in the nominative here instead of the partitive mukavaa?
In this sentence, the grammatical subject is the noun Uusi funktio. Because the adjective describes this distinct noun, it takes the nominative case (mukava). If the action itself were the subject, like in the alternative phrasing 'On mukavaa testata uusi funktio' (It is nice to test a new function), you would use the partitive mukavaa.
Even though uusi funktio is the thing being tested, why isn't it in an object case?
This is a key feature of this specific evaluative structure. The thing being evaluated (uusi funktio) is moved to the front to act as the grammatical subject of the sentence. Because it is the subject, it takes the basic nominative case instead of an object case.
Could I use the partitive case for the subject and say Uutta funktiota on mukava testata?
Yes, but the meaning shifts slightly. Using the partitive Uutta funktiota implies you are testing some part of a new function, or that the testing is an ongoing, incomplete process. Using the nominative Uusi funktio suggests testing the entire function as a complete, single action.
What verb form is testata here?
It is the 1st infinitive, which is the basic dictionary form of the verb. Whenever you use this evaluative 'is [adjective] to [verb]' structure in Finnish, the action verb always goes in this basic 1st infinitive form, just like the 'to test' form in English.