test_runner: mark module as stable

Fixes: nodejs#46642

doc/api/cli.md

@@ -1396,6 +1396,9 @@ added:
   - v18.1.0
   - v16.17.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/46983
+    description: The test runner is now stable.
   - version:
       - v19.2.0
       - v18.13.0
@@ -1412,6 +1415,10 @@ for more details.
 
 <!-- YAML
 added: v18.11.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/46983
+    description: The test runner is now stable.
 -->
 
 A regular expression that configures the test runner to only execute tests
@@ -1424,6 +1431,10 @@ whose name matches the provided pattern. See the documentation on
 added:
   - v19.6.0
   - v18.15.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/46983
+    description: The test runner is now stable.
 -->
 
 A test reporter to use when running tests. See the documentation on
@@ -1435,6 +1446,10 @@ A test reporter to use when running tests. See the documentation on
 added:
   - v19.6.0
   - v18.15.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/46983
+    description: The test runner is now stable.
 -->
 
 The destination for the corresponding test reporter. See the documentation on
@@ -1446,6 +1461,10 @@ The destination for the corresponding test reporter. See the documentation on
 added:
   - v18.0.0
   - v16.17.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/46983
+    description: The test runner is now stable.
 -->
 
 Configures the test runner to only execute top level tests that have the `only`

doc/api/test.md

@@ -6,9 +6,13 @@
 added:
   - v18.0.0
   - v16.17.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/46983
+    description: The test runner is now stable.
 -->
 
-> Stability: 1 - Experimental
+> Stability: 2 - Stable
 
 <!-- source_link=lib/test.js -->
 
@@ -377,6 +381,8 @@ internally.
 
 ## Collecting code coverage
 
+> Stability: 1 - Experimental
+
 When Node.js is started with the [`--experimental-test-coverage`][]
 command-line flag, code coverage is collected and statistics are reported once
 all tests have completed. If the [`NODE_V8_COVERAGE`][] environment variable is
@@ -533,6 +539,11 @@ The following built-reporters are supported:
   where each passing test is represented by a `.`,
   and each failing test is represented by a `X`.
 
+The exact output of these reporters is subject to change between versions of
+Node.js, and should not be relied on programmatically. If programmatic access
+to the test runner's output is required, use the events emitted by the
+{TestsStream}.
+
 ### Custom reporters
 
 [`--test-reporter`][] can be used to specify a path to custom reporter.