Create Test Intention: Fix RuntimeException on attempt to convert generated test class to Kotlin

#KT-12285 Fixed
 #EA-82281 Fixed

ChangeLog.md

@@ -168,6 +168,7 @@
 - [`KT-11933`](https://youtrack.jetbrains.com/issue/KT-11933) Entities used only by alias are marked as unused
 - [`KT-12193`](https://youtrack.jetbrains.com/issue/KT-12193) Convert to block body isn't equivalent for when expressions returning Unit
 - [`KT-10779`](https://youtrack.jetbrains.com/issue/KT-10779) Simplify 'for' using destructing declaration: intention / inspection quick fix is available only when all variables are used
+- [`KT-12285`](https://youtrack.jetbrains.com/issue/KT-12285) Fix exception on test class generation
 - [`KT-12502`](https://youtrack.jetbrains.com/issue/KT-12502) Convert to expression body should be forbidden for non-exhaustive when returning Unit
 - [`KT-12260`](https://youtrack.jetbrains.com/issue/KT-12260) ISE while replacing an operator with safe call
 

idea/src/org/jetbrains/kotlin/idea/testIntegration/KotlinCreateTestIntention.kt

@@ -180,6 +180,10 @@ class KotlinCreateTestIntention : SelfTargetingRangeIntention<KtNamedDeclaration
                                 NavigationUtil.activateFileWithPsiElement(existingClass)
                             }
                             else {
+                                with(PsiDocumentManager.getInstance(project)) {
+                                    getDocument(generatedFile)?.let { doPostponedOperationsAndUnblockDocument(it) }
+                                }
+
                                 JavaToKotlinAction.convertFiles(generatedFile.singletonList(), project, false).singleOrNull()
                             }
                         }