That is the observation that really counts.
What was tested and ruled out, your statement is ambiguous?
MOND is a specific theory which has been ruled out in several ways; look it up. It can be tuned to match galaxy rotation curves, but can't match anything else---clusters, cosmology, lensing---at the same time.
More generally, we have ruled out any possible theory in which gravity has normal visible galactic matter as the source (but some weird force law other than F = 1/r^2). The key data is the lensing and x-ray observations of the Bullet Cluster and MACS J0025.4-1222. Again, look it up. This is extremely well-publicized stuff which you ought to have known before you started ranting against dark matter.
: Dark matter is not an assumption. It is a set of observations.