This is the 5483rd most frequent Polish word.
testów
"Testów" means "of tests" in English.
In this sentence, "testów" is in the genitive plural form of "test" indicating the purpose for which the samples were sent.
Próbki zostały wysłane do laboratorium w celu testów.
The samples were sent to the laboratory for testing.
Here, "testów" again appears in the genitive plural, indicating possession as it relates to the results of these tests.
Wyniki testów były bardzo obiecujące.
The results of the tests were very promising.
In this example, "testów" is used in the genitive plural form to describe the set comprising multiple tests being prepared.