De or het testcassette?

The correct Dutch article is:

de testcassette

Rule Words ending in -te: usually de. See the rule

How to use testcassette

the testcassettede testcassette
this testcassettedeze testcassette
that testcassettedie testcassette
our testcassetteonze testcassette
your testcassettejouw testcassette
every testcassetteelke testcassette
which testcassette?welke testcassette?
a big testcassette / the big testcassetteeen grote testcassette, de grote testcassette