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+/"

2 files changed, 53 insertions, 0 deletions

diff --git a/cli/tests/unit/filter_function_test.ts b/cli/tests/unit/filter_function_test.ts
new file mode 100644
index 000000000..dd83c1dbc
--- /dev/null
+++ b/cli/tests/unit/filter_function_test.ts
@@ -0,0 +1,52 @@
+import { unitTest, assertEquals } from "./test_util.ts";
+
+// @ts-expect-error TypeScript (as of 3.7) does not support indexing namespaces by symbol
+const { createFilterFn } = Deno[Deno.internal];
+
+unitTest(function filterAsString(): void {
+  const filterFn = createFilterFn("my-test");
+  const tests = [
+    {
+      fn(): void {},
+      name: "my-test",
+    },
+    {
+      fn(): void {},
+      name: "other-test",
+    },
+  ];
+  const filteredTests = tests.filter(filterFn);
+  assertEquals(filteredTests.length, 1);
+});
+
+unitTest(function filterAsREGEX(): void {
+  const filterFn = createFilterFn("/.+-test/");
+  const tests = [
+    {
+      fn(): void {},
+      name: "my-test",
+    },
+    {
+      fn(): void {},
+      name: "other-test",
+    },
+  ];
+  const filteredTests = tests.filter(filterFn);
+  assertEquals(filteredTests.length, 2);
+});
+
+unitTest(function filterAsEscapedREGEX(): void {
+  const filterFn = createFilterFn("/\\w+-test/");
+  const tests = [
+    {
+      fn(): void {},
+      name: "my-test",
+    },
+    {
+      fn(): void {},
+      name: "other-test",
+    },
+  ];
+  const filteredTests = tests.filter(filterFn);
+  assertEquals(filteredTests.length, 2);
+});
diff --git a/cli/tests/unit/unit_tests.ts b/cli/tests/unit/unit_tests.ts
index 1701170d1..ad820a55c 100644
--- a/cli/tests/unit/unit_tests.ts
+++ b/cli/tests/unit/unit_tests.ts
@@ -24,6 +24,7 @@ import "./event_target_test.ts";
 import "./fetch_test.ts";
 import "./file_test.ts";
 import "./files_test.ts";
+import "./filter_function_test.ts";
 import "./form_data_test.ts";
 import "./format_error_test.ts";
 import "./fs_events_test.ts";