Try to fix transient issue on CI (#5017)

Same workaround as a test nearby (see #4944)

Comes from #4917, but shouldn't
be a problem

Author: alexarchambault

libs/main/test/src/mill/main/MainModuleTests.scala

@@ -208,6 +208,31 @@ object MainModuleTests extends TestSuite {
     }
 
     test("show") {
+      def checkErrStream[T](errStream: ByteArrayOutputStream)(check: String => T): T = {
+        def runCheck(): T =
+          try {
+            val strippedErr =
+              fansi.Str(errStream.toString, errorMode = fansi.ErrorMode.Sanitize).plainText
+
+            check(strippedErr)
+          } catch {
+            case ex: utest.AssertionError =>
+              pprint.err.log(errStream.toString)
+              throw ex
+          }
+
+        try runCheck()
+        catch {
+          case ex: utest.AssertionError if Properties.isWin =>
+            // On Windows, it seems there can be a delay until the messages land in errStream,
+            // it's worth retrying
+            ex.printStackTrace(System.err)
+            val waitFor = 2.seconds
+            System.err.println(s"Caught $ex, trying again in $waitFor")
+            Thread.sleep(waitFor.toMillis)
+            runCheck()
+        }
+      }
       test("single") {
         val outStream = new ByteArrayOutputStream()
         val errStream = new ByteArrayOutputStream()
@@ -233,15 +258,12 @@ object MainModuleTests extends TestSuite {
         assert(value == expected)
         assert(shown == expected)
 
-        // Make sure both stdout and stderr are redirected by `show`
-        // to stderr so that only the JSON file value goes to stdout
-        val strippedErr =
-          fansi.Str(errStream.toString, errorMode = fansi.ErrorMode.Sanitize).plainText
-
-        assert(strippedErr.contains("Hello System Stdout"))
-        assert(strippedErr.contains("Hello System Stderr"))
-        assert(strippedErr.contains("Hello Console Stdout"))
-        assert(strippedErr.contains("Hello Console Stderr"))
+        checkErrStream(errStream) { strippedErr =>
+          assert(strippedErr.contains("Hello System Stdout"))
+          assert(strippedErr.contains("Hello System Stderr"))
+          assert(strippedErr.contains("Hello Console Stdout"))
+          assert(strippedErr.contains("Hello Console Stderr"))
+        }
       }
       test("multi") {
         val outStream = new ByteArrayOutputStream()
@@ -274,37 +296,15 @@ object MainModuleTests extends TestSuite {
         assert(value == expected)
         assert(shown == expected)
 
-        def check(): Unit =
-          try {
-            // Make sure both stdout and stderr are redirected by `show`
-            // to stderr so that only the JSON file value goes to stdout
-            val strippedErr =
-              fansi.Str(errStream.toString, errorMode = fansi.ErrorMode.Sanitize).plainText
-
-            assert(strippedErr.contains("Hello System Stdout"))
-            assert(strippedErr.contains("Hello System Stderr"))
-            assert(strippedErr.contains("Hello Console Stdout"))
-            assert(strippedErr.contains("Hello Console Stderr"))
-            assert(strippedErr.contains("Hello2 System Stdout"))
-            assert(strippedErr.contains("Hello2 System Stderr"))
-            assert(strippedErr.contains("Hello2 Console Stdout"))
-            assert(strippedErr.contains("Hello2 Console Stderr"))
-          } catch {
-            case ex: utest.AssertionError =>
-              pprint.err.log(errStream.toString)
-              throw ex
-          }
-
-        try check()
-        catch {
-          case ex: utest.AssertionError if Properties.isWin =>
-            // On Windows, it seems there can be a delay until the messages land in errStream,
-            // it's worth retrying
-            ex.printStackTrace(System.err)
-            val waitFor = 2.seconds
-            System.err.println(s"Caught $ex, trying again in $waitFor")
-            Thread.sleep(waitFor.toMillis)
-            check()
+        checkErrStream(errStream) { strippedErr =>
+          assert(strippedErr.contains("Hello System Stdout"))
+          assert(strippedErr.contains("Hello System Stderr"))
+          assert(strippedErr.contains("Hello Console Stdout"))
+          assert(strippedErr.contains("Hello Console Stderr"))
+          assert(strippedErr.contains("Hello2 System Stdout"))
+          assert(strippedErr.contains("Hello2 System Stderr"))
+          assert(strippedErr.contains("Hello2 Console Stdout"))
+          assert(strippedErr.contains("Hello2 Console Stderr"))
         }
       }