<p>A number of packages on CRAN use Suggests: casually.</p>
<p>They list other packages as &quot;not required&quot; in Suggests: -- as opposed to absolutely required via Imports: or the older Depends: -- yet do not test for their use in either examples or, more commonly, unit tests.</p>
<p>So e.g. the unit tests are bound to fail because, well, Suggests != Depends.</p>
<p>This has been accomodated for many years by all parties involved by treating Suggests as a Depends and installing unconditionally. As I understand it, CRAN appears to flip a switch to automatically install all Suggests from major repositories glossing over what I consider to be a packaging shortcoming. (As an aside, treatment of Additonal_repositories: is indeed optional; Brooke Anderson and I have a fine paper under review on this)</p>
<p>I spend a fair amount of time with reverse dependency (&quot;revdep&quot;) checks of packages I maintain, and I will no longer accomodate these packages.</p>
<p>These revdep checks take long enough as it is, so I will now blacklist these packages that are guaranteed to fail when their &quot;optional&quot; dependencies are not present.</p>
<p><a href="https://cran.r-project.org/doc/manuals/r-release/R-exts.html">Writing R Extensions</a> says in <a href="https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Package-Dependencies">Section 1.1.3</a></p>
<blockquote>
<p>All packages that are needed10 to successfully run R CMD check on the package must be listed in one of ‘Depends’ or ‘Suggests’ or ‘Imports’. Packages used to run examples or tests conditionally (e.g. via <code>if(require(pkgname)))</code> should be listed in ‘Suggests’ or ‘Enhances’. (This allows checkers to ensure that all the packages needed for a complete check are installed.)</p>
<p>In particular, packages providing “only” data for examples or vignettes should be listed in ‘Suggests’ rather than ‘Depends’ in order to make lean installations possible.</p>
<p>[...]</p>
<p>It used to be common practice to use require calls for packages listed in ‘Suggests’ in functions which used their functionality, but nowadays it is better to access such functionality via :: calls.</p>
</blockquote>
<p>and continues in <a href="https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Suggested-packages">Section 1.1.3.1</a></p>
<blockquote>
<p>Note that someone wanting to run the examples/tests/vignettes may not have a suggested package available (and it may not even be possible to install it for that platform). The recommendation used to be to make their use conditional via <code>if(require(&quot;pkgname&quot;)))</code>: this is fine if that conditioning is done in examples/tests/vignettes.</p>
</blockquote>
<p>I will now exercise my option to use 'lean installations' as discussed here. If you want your package included in tests I run, please make sure it tests successfully when only its required packages are present.</p>