feat(test): Add support for regex in filter flag (#6343)

Currently, the documentation makes it sound like the test subcommand's filter
flag could accept some kind of pattern matching value like a glob or a regex,
although the function "createFilterFn" accepts a regex as an argument, there's
no way to pass an actual regex value from the CLI.

This commit makes it possible to pass a string that could be cast as regex 
when string matches "^/.*/$".

With this change, a user can use the filter flag as follow:

deno test --filter "/test-.+/"

Also tested that `\` get escaped properly, on MacOS at least, and this is 
also a valid flag:

deno test --filter "/test-\d+/"

1 files changed, 5 insertions, 0 deletions

diff --git a/cli/js/testing.ts b/cli/js/testing.ts
index e8d42c2eb..0648683a4 100644
--- a/cli/js/testing.ts
+++ b/cli/js/testing.ts
@@ -308,6 +308,9 @@ function createFilterFn(
     if (filter) {
       if (filter instanceof RegExp) {
         passes = passes && filter.test(def.name);
+      } else if (filter.startsWith("/") && filter.endsWith("/")) {
+        const filterAsRegex = new RegExp(filter.slice(1, filter.length - 1));
+        passes = passes && filterAsRegex.test(def.name);
       } else {
         passes = passes && def.name.includes(filter);
       }
@@ -325,6 +328,8 @@ function createFilterFn(
   };
 }
 
+exposeForTest("createFilterFn", createFilterFn);
+
 interface RunTestsOptions {
   exitOnFail?: boolean;
   failFast?: boolean;