Even with a lack of testing, we have other indicators to how the direction of this pandemic is proceeding. The CDC and most state health departments have re-tooled the sentinel provider reporting system, which is usually used for doctors to report "influenza-like illness" to report "COVID-like illness" directly to the CDC and state health departments. At this time, in addition to relying strictly on the positive results of the PCR test, we are also relying on doctors who have reported "presumptive" cases of COVID-19. In addition to this, the CDC has begun to roll out a self-screening tool, where people can check their symptoms, and this reports directly to the CDC when people indicate that they have mild symptoms.I can't stress this enough as well. Even tho testing is ramping up in each of the states it will be some time before we see any kind of reliable data.
Also, we have a pretty decent idea that around 15% of cases of COVID-19 lead to hospitalization. By using the number of people who are hospitalized with the disease, we can extrapolate how the outbreak is progressing. If the number of hospitalizations increases, for example- then we know that a certain percentage of the population will hopefully be managing their symptoms at home. If the number of hospitalizations decreases, then, most likely, the number of infections in the wider community has also begun to decrease.
The number one flaw with fixating too heavily on the exact numbers of confirmed cases is that people miss the point of following the trend. Don't forget, many of these tried-and-true methods of epidemiology have been developed as far back as the mid-1800s, before any laboratory diagnostic testing was available!