"we can attest" is correct and can be used in written English.
You can use it when you are affirming or verifying something, such as a statement made by someone else or a statement you have made yourself. For example, "We can attest that the software update is complete and successful."
We can attest to their deliciousness.
As scholars of the law, we can attest that the law is full of gaps and ambiguities that can bedevil the most careful thinkers.
At MEDEF, we can attest to the desire from all-sized companies across the country to engage in a dialogue where change and reform delivers true benefits to all our citizens.
We can attest that he is wary of a purely ideological approach to foreign policy and is driven by more than simple expediency in pursuit of the national interest.
As physicians who have worked in women's jails and prisons, we can attest to the fact that even the least dangerous patients are subjected to painful restrictions when taken to an outside hospital.
Apparently ignoring a recent political riot in the state of Mexico in which at least nine people were killed, Mr. Zedillo added, "We can attest that suspicions, recriminations and electoral conflicts have been resigned to history".
As we all can attest, this short poem holds true today, even after we have advanced from the lantern slides to the more common for decades 2 × 2 slides and now to PowerPoint electronic presentations.
Insofar as we can personally experience the phenomenological sequence of steps to which Heidegger refers, we ourselves can attest to the truth of his interpretation.
We know and can attest to the pain that you and your country are going through.
It is much easier – as we can all attest – to ignore it.
Seasoned mountaineers will appreciate the warmth to weight ratio as it is incredibly light, while we can personally attest to its performance on the sofa, and even in bed on a chilly night.
