Testing: record summary diagnostic

Author: henrymercer

lib/init-action.js

@@ -741,6 +741,26 @@ async function run(startedAt: Date) {
       }
     }
 
+    addDiagnostic(
+      config,
+      // Arbitrarily choose the first language. We could also choose all languages, but that
+      // increases the risk of misinterpreting the data.
+      config.languages[0],
+      makeDiagnostic(
+        "codeql-action/init/test",
+        "Test diagnostic from init action",
+        {
+          markdownMessage:
+            "This is a diagnostic to test how the diagnostic summary interacts with this PR.",
+          visibility: {
+            statusPage: false,
+            telemetry: false,
+            cliSummaryTable: true,
+          },
+        },
+      ),
+    );
+
     // Write diagnostics to the database that we previously stored in memory because the database
     // did not exist until now.
     flushDiagnostics(config);