runTests: Runs the tests associated with this Shiny app
In tomkuipers1402/shiny: Web Application Framework for R

Sources the .R files in the top-level of tests/ much like R CMD check. These files are typically simple runners for tests nested in other directories under tests/.

1	runTests(appDir = ".", filter = NULL)

`appDir`	The base directory for the application.
`filter`	If not `NULL`, only tests with file names matching this regular expression will be executed. Matching is performed on the file name including the extension.

Historically, shinytest recommended placing tests at the top-level of the tests/ directory. In order to support that model, testApp first checks to see if the .R files in the tests/ directory are all shinytests; if so, just calls out to shinytest::testApp().