A testimonial party (Dutch: beginselpartij/getuigenispartij) is a political party that focuses on its principles, instead of adapting them to local or temporal issues in the pursuit of coalition government participation.
[1] It is a peculiar phenomenon in the Netherlands, because of the Dutch system of proportional representation, in which any party that has over 0.66% of the vote can enter the House of Representatives.
As a result, most Dutch political parties will negotiate and compromise to form a coalition government.
Testimonial parties will not compromise; this, combined with the fact that they are usually small parties, makes their participation in a coalition government extremely unlikely.
Examples of parties that have referred to themselves as "testimonial" include the orthodox Protestant Reformed Political Party (SGP) and the animal rights-advocating Party for the Animals.