"serve as testimony" is correct and can be used in written English.
It is often used to refer to something, typically a document or other kind of evidence, which is used to show the truth or accuracy of a claim. For example, "A signed copy of the contract served as testimony that the agreement had been made."
I can only hope that my writings, which serve as testimony on China's present and its history, deserve that empty chair at your opening ceremony".
There are thousands of Atkins followers who have improved their health and quality of life and who serve as testimony to the effectiveness of the Atkins diet.
A mystical light behind the figures and a carefully calculated illumination of facial features serve as testimony to Mount's belief, documented in his correspondence, that music contained the seeds of virtue and could have a moralizing effect.
The large logistics applications that are used as a test bed for DARPA Ultralog serve as testimony to the ability of large agent based systems to solve some of the world's most complex tasks in grid computing.
And it will serve as testimony to the character of those who serve, and the example that you set for America and for the world.
Here are a few of his most influential pieces, which, although differing dramatically in form, all serve as testimonies to Rodchenko's radical artistic vision….
While the Labor Day parade is perhaps a shadow of the New York institution it once was -- unions no longer stage it on Labor Day because it is too difficult to drum up a crowd on the Monday of a three-day summer holiday weekend -- the presence of all six major mayoral candidates served as testimony to labor's enduring influence on New York politics, particularly in this race.
Though such statements reflected the fact that the Grand Fleet had not won the great battle its officers had sought, the peaceful surrender of the High Seas Fleet served as testimony to the strength the Grand Fleet had maintained continuously through four years of war.
Azerbaijan is stable, and the recent events, if anything, serve as a testimony that this stability is stronger than anyone trying to undermine it had presumed.
Many of the stories in "I'm So Fine" serve as a testimony to the burdens that come, in this world, with existing in a woman's body.
The charred buildings and flower-heaped barricades still crisscrossing Kiev's Independence Square – also the cradle of the 2004 Orange revolution that first shook Russia's historic hold on Ukraine – serve as poignant testimony to the more than 100 people killed during the winter.
