Measuring CMRR of op-amp circuit
To put it shortly, even if you had perfect resistors (and resistors aren't perfectly matched, so this won't even remotely work), the formula as stated is wrong.
You need to vary the input voltage and observe the variation of the output voltage; the ratio of these two differences would then be the CMRR.
Again, it's not \$\text{CMRR}=\frac{V_{out}}{V_{in}}\$; it'd be \$\text{CMRR}=\frac{\Delta V_{out}}{\Delta V_{in}}\$, because that's how much a variation of common mode input gets amplified (that's literally just the definition of amplification applied to CM input).
And again, that assumes that your resistors are all perfectly matched, which they aren't. The best resistors I can buy are 0.01% accurate, which means the differential gain isn't exactly 1, but has some unknown error, and that sadly doesn't cancel, and at CMRR &gt; 60 dB (which is pretty boring compared to what modern opamps offer), that error by far outshines our CM amplification. You'd hence need to measure that error, too, which, again, is pretty hard, because your measurement process needs to change the system much less than the CMRR, and measuring voltages does actually draw a bit of current.