diff --git a/platform/diff-impl/tests/testSrc/com/intellij/diff/merge/MergeTestBase.kt b/platform/diff-impl/tests/testSrc/com/intellij/diff/merge/MergeTestBase.kt
index 3f7b40904c49..f2e46c272305 100644
--- a/platform/diff-impl/tests/testSrc/com/intellij/diff/merge/MergeTestBase.kt
+++ b/platform/diff-impl/tests/testSrc/com/intellij/diff/merge/MergeTestBase.kt
@@ -59,6 +59,7 @@ abstract class MergeTestBase : HeavyDiffTestCase() {
     val viewer = TextMergeTool.INSTANCE.createComponent(context, request) as TextMergeViewer
     try {
       val toolbar = viewer.init()
+      viewer.viewer.rediff()
       UIUtil.dispatchAllInvocationEvents()
 
       val builder = TestBuilder(viewer, toolbar.toolbarActions ?: emptyList())
diff --git a/platform/diff-impl/tests/testSrc/com/intellij/openapi/diff/impl/settings/DiffColorSettingsTest.kt b/platform/diff-impl/tests/testSrc/com/intellij/openapi/diff/impl/settings/DiffColorSettingsTest.kt
index 5828b5884cdb..f9bbae5f66c3 100644
--- a/platform/diff-impl/tests/testSrc/com/intellij/openapi/diff/impl/settings/DiffColorSettingsTest.kt
+++ b/platform/diff-impl/tests/testSrc/com/intellij/openapi/diff/impl/settings/DiffColorSettingsTest.kt
@@ -27,6 +27,7 @@ class DiffColorSettingsTest : HeavyDiffTestCase() {
     try {
       panel = DiffPreviewPanel()
       val viewer = panel.testGetViewer()
+      viewer.rediff()
 
       assertEquals(viewer.changes.size, 6)
       assertContainsRange(viewer, TextDiffType.MODIFIED)