Fixes for local testing issues (#132)

* Using the default plot device was causing `devtools::test()` to create a bunch of plot files in the test directory. I don't think there's any reason to use the default plot device (since that may lead to windows popping up for the user), so we just switch to using `pdf(NULL)` everywhere
* There was one test that used `dev.new()` to start a new device; there I made sure that the new device was always a quiet `pdf()` device.
* I also fixed a partial argument match warning that was causing a local test failure for me since I have `options(warnPartialMatchArgs = TRUE)`
* Add a test for plotmath too (to ensure that (e.g.) we can compute string widths)

R/eval.R

@@ -69,10 +69,9 @@ evaluate <- function(input,
   }
 
   if (new_device) {
-    # Start new graphics device and clean up afterwards
-    if (identical(grDevices::pdf, getOption("device"))) {
-      dev.new(file = NULL)
-    } else dev.new()
+    # Ensure we have a graphics device available for recording, but choose
+    # one that's available on all platforms and doesn't write to disk
+    pdf(file = NULL)
     dev.control(displaylist = "enable")
     dev <- dev.cur()
     on.exit(dev.off(dev))

tests/testthat/plot-persp.R

@@ -1,4 +1,4 @@
-x <- seq(-10, 10, length = 30)
+x <- seq(-10, 10, length.out = 30)
 y <- x
 ff <- function(x,y) { r <- sqrt(x^2 + y^2); 10 * sin(r) / r }
 z <- outer(x, y, ff)

tests/testthat/test-graphics.R

@@ -132,14 +132,14 @@ test_that("by default, evaluate() always records plots regardless of the device"
 })
 
 test_that("Rplots.pdf files are not created", {
-  op <- options(device = pdf)
-  on.exit(options(op))
-  evaluate(file("plot.R"))
+  ev <- evaluate("plot(1)")
   expect_false(file.exists("Rplots.pdf"))
 })
 
 # https://github.com/yihui/knitr/issues/2297
 test_that("existing plots will not leak into evaluate()", {
+  withr::local_options(device = function() pdf(NULL))
+
   pdf(NULL)
   dev.control('enable')
   d <- dev.cur()