It is my great pleasure to acknowledge many fruitful discussions and collaborations with a number of people that have shaped my ideas on astrophysical tests of strong-field gravity. In particular, I thank T. Belloni, D. Chakrabarty, S. DeDeo, F. Lamb, C. Miller, R. Narayan, J. McClintock, F. Özel and M. van der Klis. I am indebted to S. DeDeo and F. Özel for helping me settle on and understand the definition of strong-field gravity. I am also grateful to G. Esposito-Farèse, T. Johanssen, J. McClintock, F. Özel and C. Reynolds for their detailed comments that helped me greatly improve the presentation of this review.
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