https://www.businessinsider.com/us-coronavirus-testing-problems-timeline-2020-3#the-us-test-was-approved-by-the-food-and-drug-administration-on-february-4-around-two-weeks-after-the-first-case-was-reported-in-washington-and-more-than-a-month-after-the-outbreak-was-first-reported-in-china-6
The initial outbreak was first reported in China on December 31. By January 10, a Shanghai laboratory had sequenced the virus' genome.
German scientists produced the first diagnostic test a week later.
The World Health Organization began shipping those tests out to countries during the first week of February.
The US opted to develop its own test, but the distribution was limited.
The US test was approved by the Food and Drug Administration on February 4 — around two weeks after the first case was reported in Washington and more than a month after the outbreak was first reported in China.
A problem with one ingredient in the US tests caused more than half of state labs to receive inconclusive results.