I have 3 groups (n=5 per group) from biological data. I have checked the normality of my groups using the Shapiro-Wilk test and two of my groups are normally distributed. However, the 3rd group values are all zero, thus there is no variability in that group. The data I have is discrete and it can never be negative value as I am measuring number of worms in my experiments. Should I use a parametric test (ANOVA) or a non-parametric test (Kruskal-Wallis) test to compare the 3 groups?

Other research groups with similar data have done an ANOVA but I am not 100% sure why they consider the group with all zeros to be normally distributed. Here is an example: https://www.ncbi.nlm.nih.gov/pubmed/29540816 Figure 2a - "sub-group 3" has values all equal to zero and is compared with one-way ANOVA to "sham" group

Disclaimer : I am not great with stats but all help is appreciated!