Fix CI problems (#268)

* correctly protect against non existence

* Don't use random port

* skip preview tests on CI

they are passing but they make CI hang

Author: cderv

tests/testthat/test-preview.R

@@ -1,6 +1,7 @@
 test_that("quarto_preview default functionality", {
   skip_if_no_quarto()
   skip_on_cran()
+  skip_on_ci()
 
   tmp_dir <- withr::local_tempdir()
   withr::local_dir(tmp_dir)
@@ -23,22 +24,29 @@ test_that("quarto_preview default functionality", {
 test_that("quarto_preview can change port", {
   skip_if_no_quarto()
   skip_on_cran()
+  skip_on_ci()
 
   tmp_dir <- withr::local_tempdir()
   withr::local_dir(tmp_dir)
   xfun::write_utf8(c("---", "title: Test", "---", "", "# Hello"), "test.qmd")
 
+  known_port <- find_port()
   expect_no_error({
-    url <- withr::with_dir(tmp_dir, {
-      quarto_preview("test.qmd", port = 8888, browse = FALSE, quiet = TRUE)
+    preview_url <- withr::with_dir(tmp_dir, {
+      quarto_preview(
+        "test.qmd",
+        port = known_port,
+        browse = FALSE,
+        quiet = TRUE
+      )
     })
   })
 
   # Always clean up
   withr::defer(quarto_preview_stop())
 
-  if (exists("url")) {
-    expect_true(grepl("^https?://", url))
-    expect_true(grepl(":8888", url))
-  }
+  skip_if(!exists("preview_url", inherits = FALSE))
+  skip_if(!is.character(preview_url))
+  expect_true(grepl("^https?://", preview_url))
+  expect_true(grepl(sprintf(":%s", known_port), preview_url))
 })