Predictions of many theories differ only in strong field regimes
Pulsar provide strong field tests
Solar system only provides weak field tests
Shapiro delay
Einstein delay
Existence of gravitational waves
Observations and GR agree to better than 1%
Constancy of Chandrasekhar mass
Ultra low freq gravitational waves and cosmic strings
Strong equivalence principle
Invariance of Lorentz transformations
Conservations laws
Most precise null tests of fundamental physics