add fix for skip outside test

Author: kevinushey

NEWS.md

@@ -1,5 +1,8 @@
 # testthat (development version)
 
+* Fixed an issue where calling `skip()` outside of a test could cause
+  an unexpected error (@kevinushey, #2038).
+
 # testthat 3.2.2
 
 ## New expectations

R/snapshot-reporter.R

@@ -116,7 +116,7 @@ SnapshotReporter <- R6::R6Class("SnapshotReporter",
     },
 
     add_result = function(context, test, result) {
-      if (is.null(self$test)) {
+      if (!length(self$test)) {
         return()
       }