R Under development (unstable) (2025-09-17 r88852 ucrt) -- "Unsuffered Consequences"
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> library(testthat)
> library(did2s)
Loading required package: fixest
did2s (v1.2.0). For more information on the methodology, visit <https://www.kylebutts.github.io/did2s>

To cite did2s in publications use:

  Butts & Gardner, "The R Journal: did2s: Two-Stage
  Difference-in-Differences", The R Journal, 2022

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {did2s: Two-Stage Difference-in-Differences Following Gardner (2021)},
    author = {Kyle Butts and John Gardner},
    year = {2021},
    url = {https://journal.r-project.org/articles/RJ-2022-048/},
  }


> 
> test_check("did2s")
! curl package not installed, falling back to using `url()`
Note these estimators rely on different underlying assumptions. See Table 2 of `https://arxiv.org/abs/2109.05913` for an overview.
The variable 'x3' has been removed because of collinearity (see $collin.var).
[ FAIL 0 | WARN 1 | SKIP 0 | PASS 29 ]

[ FAIL 0 | WARN 1 | SKIP 0 | PASS 29 ]
> 
> proc.time()
   user  system elapsed 
  11.89    1.46   13.87