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+/"

cli/flags.rs

@@ -1105,7 +1105,7 @@ fn test_subcommand<'a, 'b>() -> App<'a, 'b> {
       Arg::with_name("filter")
         .long("filter")
         .takes_value(true)
-        .help("Run tests with this string in the test name"),
+        .help("Run tests with this string or pattern in the test name"),
     )
     .arg(
       Arg::with_name("files")

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;

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);
+});

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";

docs/testing.md

@@ -129,10 +129,33 @@ There are a number of options to filter the tests you are running.
 Tests can be run individually or in groups using the command line `--filter`
 option.
 
-```shell
+The filter flags accept a string or a pattern as value.
-deno test --filter "hello world" tests/
+
+Assuming the following tests:
+
+```ts
+Deno.test({ name: "my-test", fn: myTest });
+Deno.test({ name: "test-1", fn: test1 });
+Deno.test({ name: "test2", fn: test2 });
 ```
 
+This command will run all of these tests because they all contain the word
+"test".
+
+```shell
+deno test --filter "test" tests/
+```
+
+On the flip side, the following command uses a pattern and will run the second
+and third tests.
+
+```shell
+deno test --filter "/test-*\d/" tests/
+```
+
+_To let Deno know that you want to use a pattern, wrap your filter with
+forward-slashes like the JavaScript syntactic sugar for a REGEX._
+
 This command will run any test which contains the string "hello world" in its
 test name for tests found within files in the `tests/` directory.