Fix rare count_test edge case (#2)

DESCRIPTION

@@ -1,7 +1,7 @@
 Encoding: UTF-8
 Package: covr
 Title: Test Coverage for Packages
-Version: 3.6.5.9000
+Version: 3.6.5.9001
 Authors@R: c(
     person("Jim", "Hester", email = "james.f.hester@gmail.com", role = c("aut", "cre")),
     person("Willem", "Ligtenberg", role = "ctb"),

NEWS.md

@@ -1,5 +1,8 @@
 # covr (development version)
 
+* Fix a rare edge case where `count_test` was called before `.current_test` has
+  been initialized leading to crash (@maksymiuks).
+
 # covr 3.6.5
 
 ## New Features and improvements

R/trace_tests.R

@@ -114,6 +114,11 @@ count_test <- function(key) {
     tests$tally <- rbind(tests$tally, matrix(NA_integer_, ncol = 4L, nrow = n))
   }
 
+  # ignore if .current_test was not initialized properly yet
+  if (length(.current_test$index) == 0) {
+    return()
+  }
+
   # test number
   tests$.data[[1L]] <- .current_test$index