Comparison of tests of General Relativity, inspired by Psaltis (2004). Shown in black are well-established tests: the Pound & Rebka (1959) experiment, the precession of Mercury (Einstein 1916), light deflection and the Shapiro delay in the solar system, the Hulse-Taylor pulsar (Taylor & Weisberg 1982), the gravitational redshift of Sirius B (Greenstein et al. 1971; Barstow et al. 2005), the LIGO detections (Abbott et al. 2016a,c,b), and the relativistic Fe Kα line (Tanaka et al. 1995; Fabian et al. 2000). Future tests are shown in grey, and this work, which uses the S2 orbit around Sgr A^✻, is shown in blue.