load_baseline_incidence

[Hanmeng-Xu]

Tests:

1. check if the country_baseline raster and pop_baseline are of the same extent, if not, return a warning message;
2. maybe a message in the middle displaying the mean and standard deviation of the distribution;
3. the length of incid1 should be the same as the number of admin1, and the length of incid2 should be the same as the number of admin2. If not should return an error message;
4. the length of pop1 should be the same as the number of admin1 and the length of pop2 should be the same as the number of admin2 .
5. confirm_rate_raster_one_layer and raster1_template (or country_baseline[[1]]) should have the same resolution and the same extent, if not should return an error message;
6. observed_case_raster and raster1_template (or country_baseline[[1]]) should have the same resolution and the same extent.