Resolve "suppressWarnings()" in snapshot tests

[ItsMeKathy]

For the tests for volcano plot and histogram, "suppressWarnings()" is used for now because of the warnings:

• volcano plot: "Removed 6 rows containing missing values or values outside the scale range (geom_point())."
• histogram: "Removed 5 rows containing non-finite outside the scale range (stat_bin())."

Maybe filtering the results of the t-test/ANOVA?