Test

a <- 3; b <- 5; testthat::expect_equal(a, b)

## Error: a not equal to b
## Mean relative difference: 0.4

a <- "3"; b <- "5"; testthat::expect_equal(a, b)

## Error: a not equal to b
## 1 string mismatches:
## x[1]: 5
## y[1]: 3

Session info

sessionInfo()

## R version 3.0.2 (2013-09-25)
## Platform: x86_64-pc-linux-gnu (64-bit)
## 
## locale:
##  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
##  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
##  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
##  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
##  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
## 
## attached base packages:
## [1] stats     graphics  grDevices utils     datasets  methods   base     
## 
## other attached packages:
## [1] knitr_1.5.13
## 
## loaded via a namespace (and not attached):
## [1] digest_0.6.3      evaluate_0.5.1    formatR_0.10.3    stringr_0.6.2    
## [5] testthat_0.7.1.99 tools_3.0.2