diff --git a/java/testFramework/src/com/intellij/codeInsight/daemon/DaemonAnalyzerTestCase.java b/java/testFramework/src/com/intellij/codeInsight/daemon/DaemonAnalyzerTestCase.java
index 4d921d5d9454..14e3931eb283 100644
--- a/java/testFramework/src/com/intellij/codeInsight/daemon/DaemonAnalyzerTestCase.java
+++ b/java/testFramework/src/com/intellij/codeInsight/daemon/DaemonAnalyzerTestCase.java
@@ -25,6 +25,8 @@ import com.intellij.openapi.application.ex.PathManagerEx;
 import com.intellij.openapi.command.WriteCommandAction;
 import com.intellij.openapi.editor.Document;
 import com.intellij.openapi.editor.Editor;
+import com.intellij.openapi.progress.ProgressManager;
+import com.intellij.openapi.progress.impl.CoreProgressManager;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.roots.ModuleRootManager;
 import com.intellij.openapi.startup.StartupManager;
@@ -41,6 +43,7 @@ import com.intellij.psi.impl.source.resolve.reference.ReferenceProvidersRegistry
 import com.intellij.psi.xml.XmlFileNSInfoProvider;
 import com.intellij.testFramework.*;
 import com.intellij.testFramework.fixtures.impl.CodeInsightTestFixtureImpl;
+import com.intellij.util.ThrowableRunnable;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.xml.XmlSchemaProvider;
 import it.unimi.dsi.fastutil.ints.IntArrayList;
@@ -109,6 +112,16 @@ public abstract class DaemonAnalyzerTestCase extends JavaCodeInsightTestCase {
     }
   }
 
+  // when running very long tasks (e.g. during stress/perf tests) CoreProgressManager might decide to de-prioritize background processes,
+  // defeating the whole purpose. Do not let him do that.
+  @Override
+  protected void runTestRunnable(@NotNull ThrowableRunnable<Throwable> testRunnable) throws Throwable {
+    ((CoreProgressManager)ProgressManager.getInstance()).<Void, Throwable>suppressAllDeprioritizationsDuringLongTestsExecutionIn(()-> {
+      super.runTestRunnable(testRunnable);
+      return null;
+    });
+  }
+
   protected final void enableInspectionTool(@NotNull InspectionProfileEntry tool) {
     InspectionsKt.enableInspectionTool(getProject(), tool, getTestRootDisposable());
   }
diff --git a/platform/core-impl/src/com/intellij/openapi/progress/impl/CoreProgressManager.java b/platform/core-impl/src/com/intellij/openapi/progress/impl/CoreProgressManager.java
index f07a6a42a72a..2810a694bd12 100644
--- a/platform/core-impl/src/com/intellij/openapi/progress/impl/CoreProgressManager.java
+++ b/platform/core-impl/src/com/intellij/openapi/progress/impl/CoreProgressManager.java
@@ -839,7 +839,7 @@ public class CoreProgressManager extends ProgressManager implements Disposable {
   }
 
   protected boolean sleepIfNeededToGivePriorityToAnotherThread() {
-    if (!isCurrentThreadEffectivelyPrioritized() && isLowPriorityReallyApplicable()) {
+    if (isDeprioritizationEnabled() && !isCurrentThreadEffectivelyPrioritized() && isLowPriorityReallyApplicable()) {
       LockSupport.parkNanos(1_000_000);
       avoidBlockingPrioritizingThread();
       return true;
@@ -919,6 +919,21 @@ public class CoreProgressManager extends ProgressManager implements Disposable {
     return false;
   }
 
+  private boolean isDeprioritizationEnabled() {
+    return myDeprioritizations.get() < 1_000_000;
+  }
+  @TestOnly
+  @ApiStatus.Internal
+  public <T,E extends Throwable> T suppressAllDeprioritizationsDuringLongTestsExecutionIn(@NotNull ThrowableComputable<T, E> runnable) throws E {
+    myDeprioritizations.addAndGet(1_000_000);
+    try {
+      return runnable.compute();
+    }
+    finally {
+      myDeprioritizations.addAndGet(-1_000_000);
+    }
+  }
+
   @NotNull
   public static ModalityState getCurrentThreadProgressModality() {
     ProgressIndicator indicator = threadTopLevelIndicators.get(Thread.currentThread().getId());
diff --git a/platform/testFramework/src/com/intellij/testFramework/fixtures/impl/CodeInsightTestFixtureImpl.java b/platform/testFramework/src/com/intellij/testFramework/fixtures/impl/CodeInsightTestFixtureImpl.java
index fc0fae47659e..77138cfe4a28 100644
--- a/platform/testFramework/src/com/intellij/testFramework/fixtures/impl/CodeInsightTestFixtureImpl.java
+++ b/platform/testFramework/src/com/intellij/testFramework/fixtures/impl/CodeInsightTestFixtureImpl.java
@@ -84,6 +84,8 @@ import com.intellij.openapi.fileTypes.FileTypeManager;
 import com.intellij.openapi.module.Module;
 import com.intellij.openapi.module.ModuleManager;
 import com.intellij.openapi.progress.ProcessCanceledException;
+import com.intellij.openapi.progress.ProgressManager;
+import com.intellij.openapi.progress.impl.CoreProgressManager;
 import com.intellij.openapi.project.DumbService;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.roots.ModuleRootManager;
@@ -257,48 +259,50 @@ public class CodeInsightTestFixtureImpl extends BaseFixture implements CodeInsig
     DaemonCodeAnalyzerSettings settings = DaemonCodeAnalyzerSettings.getInstance();
     ProjectInspectionProfileManager.getInstance(project); // avoid "severities changed, restart" event
 
-    ProcessCanceledException exception = null;
-    int retries = 1000;
-    for (int i = 0; i < retries; i++) {
-      int oldDelay = settings.getAutoReparseDelay();
-      try {
-        settings.setAutoReparseDelay(0);
-        List<HighlightInfo> infos = new ArrayList<>();
-        EdtTestUtil.runInEdtAndWait(() -> {
-          codeAnalyzer.runPasses(file, editor.getDocument(), Collections.singletonList(textEditor), toIgnore, canChangeDocument, null);
-          IdeaTestExecutionPolicy policy = IdeaTestExecutionPolicy.current();
-          if (policy != null) {
-            policy.waitForHighlighting(project, editor);
-          }
-          IdentifierHighlighterPassFactory.waitForIdentifierHighlighting();
-          infos.addAll(DaemonCodeAnalyzerImpl.getHighlights(editor.getDocument(), null, project));
-          if (readEditorMarkupModel) {
-            MarkupModelEx markupModel = (MarkupModelEx)editor.getMarkupModel();
-            DaemonCodeAnalyzerEx.processHighlights(markupModel, project, null, 0, editor.getDocument().getTextLength(),
-                                                   Processors.cancelableCollectProcessor(infos));
-          }
-        });
-        infos.addAll(DaemonCodeAnalyzerEx.getInstanceEx(project).getFileLevelHighlights(project, file));
-        return infos;
-      }
-      catch (ProcessCanceledException e) {
-        Throwable cause = e.getCause();
-        if (cause != null && cause.getClass() != Throwable.class) {
-          // canceled because of an exception, no need to repeat the same
-          throw e;
+    return ((CoreProgressManager)ProgressManager.getInstance()).suppressAllDeprioritizationsDuringLongTestsExecutionIn(() -> {
+      ProcessCanceledException exception = null;
+      int retries = 1000;
+      for (int i = 0; i < retries; i++) {
+        int oldDelay = settings.getAutoReparseDelay();
+        try {
+          settings.setAutoReparseDelay(0);
+          List<HighlightInfo> infos = new ArrayList<>();
+          EdtTestUtil.runInEdtAndWait(() -> {
+            codeAnalyzer.runPasses(file, editor.getDocument(), Collections.singletonList(textEditor), toIgnore, canChangeDocument, null);
+            IdeaTestExecutionPolicy policy = IdeaTestExecutionPolicy.current();
+            if (policy != null) {
+              policy.waitForHighlighting(project, editor);
+            }
+            IdentifierHighlighterPassFactory.waitForIdentifierHighlighting();
+            infos.addAll(DaemonCodeAnalyzerImpl.getHighlights(editor.getDocument(), null, project));
+            if (readEditorMarkupModel) {
+              MarkupModelEx markupModel = (MarkupModelEx)editor.getMarkupModel();
+              DaemonCodeAnalyzerEx.processHighlights(markupModel, project, null, 0, editor.getDocument().getTextLength(),
+                                                     Processors.cancelableCollectProcessor(infos));
+            }
+          });
+          infos.addAll(DaemonCodeAnalyzerEx.getInstanceEx(project).getFileLevelHighlights(project, file));
+          return infos;
         }
+        catch (ProcessCanceledException e) {
+          Throwable cause = e.getCause();
+          if (cause != null && cause.getClass() != Throwable.class) {
+            // canceled because of an exception, no need to repeat the same
+            throw e;
+          }
 
-        EdtTestUtil.runInEdtAndWait(() -> {
-          PsiDocumentManager.getInstance(project).commitAllDocuments();
-          UIUtil.dispatchAllInvocationEvents();
-        });
-        exception = e;
+          EdtTestUtil.runInEdtAndWait(() -> {
+            PsiDocumentManager.getInstance(project).commitAllDocuments();
+            UIUtil.dispatchAllInvocationEvents();
+          });
+          exception = e;
+        }
+        finally {
+          settings.setAutoReparseDelay(oldDelay);
+        }
       }
-      finally {
-        settings.setAutoReparseDelay(oldDelay);
-      }
-    }
-    throw new AssertionError("Unable to highlight after " + retries + " retries", exception);
+      throw new AssertionError("Unable to highlight after " + retries + " retries", exception);
+    });
   }
 
   public static void ensureIndexesUpToDate(@NotNull Project project) {