What I should've said is that the specimen validity test doesn't test whether urine is human or not.
Bullshit! The specimen validity test checks for 3 conditions:

A) If a sample is adulterated (use of drop-in additives, or household chemicals)

B) If a sample is diluted (low creatinine and specific gravity levels)

C) If a substituted specimen has been used (creatinine and specific gravity levels that are so low and/or divergent that its not consistent with normal human urine)

There is another test that can distinguish human from synthetic urine,
There is no test for this without getting to the area of genetic testing. Not only is genetic testing costly and complicated in process, but labs practicing in the US are prohibited by law from performing any form of genetic testing on urine samples collected for a drug test. Not unless explicit permission was granted by the donor on an entirely seperate and detailed consent form.

The labs are only allowed to test for drug metabolites, creatinine, pH, specific gravity, certain oxidants, and excessive nitrites. And under this criteria (established by the US Dept of Health & Human Services) a "non-human" sample is ruled when when the creatinine concentration is less than 2mg/dL, and the specific gravity is less than or equal to 1.0010; or greater than or equal to 1.0200 on both the initial and confirmatory creatinine tests (i.e., the same colorimetric test may be used to test both aliquots) and on both the initial and confirmatory specific gravity tests (i.e., a refractometer is used to test both aliquots) on two separate aliquots.

And like I earlier stated, as long as the synthetic batch is not expired and had been stored away from direct sunlight, it will pass these validity checks.