Verify that tests haven't written anything in the System.out (#2882)

* Remove LF tests, each test has its stress on lincheck counterpart
* Adjust failing tests, allow junit4 test printing to console

Author: qwwdfsad

kotlinx-coroutines-core/jvm/test/FieldWalker.kt

@@ -11,7 +11,6 @@ import java.util.*
 import java.util.Collections.*
 import java.util.concurrent.atomic.*
 import java.util.concurrent.locks.*
-import kotlin.collections.ArrayList
 import kotlin.test.*
 
 object FieldWalker {
@@ -154,8 +153,9 @@ object FieldWalker {
         while (true) {
             val fields = type.declaredFields.filter {
                 !it.type.isPrimitive
-                        && (statics || !Modifier.isStatic(it.modifiers))
-                        && !(it.type.isArray && it.type.componentType.isPrimitive)
+                    && (statics || !Modifier.isStatic(it.modifiers))
+                    && !(it.type.isArray && it.type.componentType.isPrimitive)
+                    && it.name != "previousOut" // System.out from TestBase that we store in a field to restore later
             }
             fields.forEach { it.isAccessible = true } // make them all accessible
             result.addAll(fields)

kotlinx-coroutines-core/jvm/test/TestBase.kt

@@ -7,11 +7,10 @@ package kotlinx.coroutines
 import kotlinx.coroutines.internal.*
 import kotlinx.coroutines.scheduling.*
 import org.junit.*
-import java.lang.Math.*
+import java.io.*
 import java.util.*
 import java.util.concurrent.atomic.*
 import kotlin.coroutines.*
-import kotlin.math.*
 import kotlin.test.*
 
 private val VERBOSE = systemProp("test.verbose", false)
@@ -23,13 +22,13 @@ public actual val isStressTest = System.getProperty("stressTest")?.toBoolean() ?
 
 public val stressTestMultiplierSqrt = if (isStressTest) 5 else 1
 
+private const val SHUTDOWN_TIMEOUT = 1_000L // 1s at most to wait per thread
+
 /**
  * Multiply various constants in stress tests by this factor, so that they run longer during nightly stress test.
  */
 public actual val stressTestMultiplier = stressTestMultiplierSqrt * stressTestMultiplierSqrt
 
-public val stressTestMultiplierCbrt = cbrt(stressTestMultiplier.toDouble()).roundToInt()
-
 @Suppress("ACTUAL_WITHOUT_EXPECT")
 public actual typealias TestResult = Unit
 
@@ -52,7 +51,10 @@ public actual typealias TestResult = Unit
  * }
  * ```
  */
-public actual open class TestBase actual constructor() {
+public actual open class TestBase(private var disableOutCheck: Boolean)  {
+
+    actual constructor(): this(false)
+
     public actual val isBoundByJsTestTimeout = false
     private var actionIndex = AtomicInteger()
     private var finished = AtomicBoolean()
@@ -62,9 +64,15 @@ public actual open class TestBase actual constructor() {
     private lateinit var threadsBefore: Set<Thread>
     private val uncaughtExceptions = Collections.synchronizedList(ArrayList<Throwable>())
     private var originalUncaughtExceptionHandler: Thread.UncaughtExceptionHandler? = null
-    private val SHUTDOWN_TIMEOUT = 1_000L // 1s at most to wait per thread
+    /*
+     * System.out that we redefine in order to catch any debugging/diagnostics
+     * 'println' from main source set.
+     * NB: We do rely on the name 'previousOut' in the FieldWalker in order to skip its
+     * processing
+     */
+    private lateinit var previousOut: PrintStream
 
-    /**
+        /**
      * Throws [IllegalStateException] like `error` in stdlib, but also ensures that the test will not
      * complete successfully even if this exception is consumed somewhere in the test.
      */
@@ -117,7 +125,7 @@ public actual open class TestBase actual constructor() {
     }
 
     /**
-     * Asserts that this it the last action in the test. It must be invoked by any test that used [expect].
+     * Asserts that this is the last action in the test. It must be invoked by any test that used [expect].
      */
     public actual fun finish(index: Int) {
         expect(index)
@@ -137,6 +145,16 @@ public actual open class TestBase actual constructor() {
         finished.set(false)
     }
 
+    private object TestOutputStream : PrintStream(object : OutputStream() {
+        override fun write(b: Int) {
+            error("Detected unexpected call to 'println' from source code")
+        }
+    })
+
+    fun println(message: Any?) {
+        previousOut.println(message)
+    }
+
     @Before
     fun before() {
         initPoolsBeforeTest()
@@ -147,6 +165,10 @@ public actual open class TestBase actual constructor() {
             e.printStackTrace()
             uncaughtExceptions.add(e)
         }
+        if (!disableOutCheck) {
+            previousOut = System.out
+            System.setOut(TestOutputStream)
+        }
     }
 
     @After
@@ -158,14 +180,17 @@ public actual open class TestBase actual constructor() {
         }
         // Shutdown all thread pools
         shutdownPoolsAfterTest()
-        // Check that that are now leftover threads
+        // Check that are now leftover threads
         runCatching {
             checkTestThreads(threadsBefore)
         }.onFailure {
             setError(it)
         }
         // Restore original uncaught exception handler
         Thread.setDefaultUncaughtExceptionHandler(originalUncaughtExceptionHandler)
+        if (!disableOutCheck) {
+            System.setOut(previousOut)
+        }
         if (uncaughtExceptions.isNotEmpty()) {
             makeError("Expected no uncaught exceptions, but got $uncaughtExceptions")
         }