This study warns that limited testing rates because of limited testing ability can cause models to give incorrect results.

We need reliable estimates of the COVID-19 epidemic growth rate to guide the timing and intensity of intervention strategies. A number of studies have quantified the growth rate using time-series of reported cases during early phases of the outbreak. They use this to calculate the basic reproduction number, R0, which refers to the number of secondary cases infected by each index case

Researchers illustrated how epidemic curves of reported cases don’t always reflect the true epidemic growth rate because of variable testing rates. If you test less, you find less disease.