diff --git a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestCompiler.kt b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestCompiler.kt
index e98c8e8b861..21b50ad96d9 100644
--- a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestCompiler.kt
+++ b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestCompiler.kt
@@ -175,9 +175,13 @@ internal sealed interface TestCompilationResult {
             is DependencyFailures -> fail { describeDependencyFailures() }
         }
 
-        private fun Failure.describeFailure() = when (this) {
-            is CompilerFailure -> "Compilation failed.\n\n$loggedData"
-            is UnexpectedFailure -> "Compilation failed with unexpected exception.\n\n$loggedData"
+        private fun Failure.describeFailure() = buildString {
+            when (this@describeFailure) {
+                is CompilerFailure -> appendLine("Compilation failed.")
+                is UnexpectedFailure -> appendLine("Compilation failed with unexpected exception.")
+            }
+            appendLine()
+            appendLine(loggedData)
         }
 
         private fun DependencyFailures.describeDependencyFailures() =
diff --git a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestRunner.kt b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestRunner.kt
index 24d3882fac5..e0d4e59869f 100644
--- a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestRunner.kt
+++ b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/TestRunner.kt
@@ -109,8 +109,11 @@ private class TestOutput(
 
     private inline fun <T> verifyExpectation(expected: T, actual: T, crossinline errorMessageHeader: () -> String) {
         assertEquals(expected, actual) {
-            val loggedTestRun = LoggedData.TestRun(loggedParameters, exitCode, stdOut, stdErr, finishTimeMillis - startTimeMillis)
-            "${errorMessageHeader()}\n\n$loggedTestRun"
+            """
+                ${errorMessageHeader()}
+
+                ${LoggedData.TestRun(loggedParameters, exitCode, stdOut, stdErr, finishTimeMillis - startTimeMillis)}
+            """.trimIndent()
         }
     }
 
diff --git a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/group/TestCaseGroupProvider.kt b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/group/TestCaseGroupProvider.kt
index 9bce95baa08..614998a7253 100644
--- a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/group/TestCaseGroupProvider.kt
+++ b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/group/TestCaseGroupProvider.kt
@@ -67,7 +67,11 @@ internal class StandardTestCaseGroupProvider(private val environment: TestEnviro
             // Don't register new test module if there is another one with the same name.
             val testModule = testModules.getOrPut(newTestModule.name) { newTestModule }
             assertTrue(testModule === newTestModule || testModule.haveSameSymbols(newTestModule)) {
-                "$location: Two declarations of the same module with different dependencies or friends found:\n$testModule\n$newTestModule"
+                """
+                    $location: Two declarations of the same module with different dependencies or friends found:
+                    $testModule
+                    $newTestModule
+                """.trimIndent()
             }
 
             currentTestModule = testModule
@@ -111,7 +115,13 @@ internal class StandardTestCaseGroupProvider(private val environment: TestEnviro
                     directivesParser.convertToRegisteredDirective(rawDirective)
                 } catch (e: AssertionError) {
                     // Enhance error message with concrete test data file and line number where the error has happened.
-                    throw AssertionError("$location: Error while parsing directive in test data file.\nCause: ${e.message}", e)
+                    throw AssertionError(
+                        """
+                            $location: Error while parsing directive in test data file.
+                            Cause: ${e.message}
+                        """.trimIndent(),
+                        e
+                    )
                 }
 
                 if (parsedDirective != null) {
@@ -228,8 +238,10 @@ internal class StandardTestCaseGroupProvider(private val environment: TestEnviro
                         && existingPackageName[packageName.length] == '.')
             ) {
                 val location = Location(testDataFile, existingPackageDeclarationLineNumber)
-                "$location: Invalid package name declaration found: $existingPackageDeclarationLine\nExpected: package $packageName"
-
+                """
+                    $location: Invalid package name declaration found: $existingPackageDeclarationLine
+                    Expected: package $packageName
+                """.trimIndent()
             }
             text
         } else
diff --git a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/Files.kt b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/Files.kt
index 53a199d253d..3b0f728810b 100644
--- a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/Files.kt
+++ b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/Files.kt
@@ -19,7 +19,11 @@ internal fun getAbsoluteFile(localPath: String): File = File(getHomeDirectory())
 
 internal fun computeGeneratedSourcesDir(testDataBaseDir: File, testDataFile: File, generatedSourcesBaseDir: File): File {
     assertTrue(testDataFile.startsWith(testDataBaseDir)) {
-        "The file is outside of the directory.\nFile: $testDataFile\nDirectory: $testDataBaseDir"
+        """
+            The file is outside of the directory.
+            File: $testDataFile
+            Directory: $testDataBaseDir
+        """.trimIndent()
     }
 
     val testDataFileDir = testDataFile.parentFile
diff --git a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/PackageNames.kt b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/PackageNames.kt
index 7dc369668f8..07393003efb 100644
--- a/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/PackageNames.kt
+++ b/native/native.tests/tests/org/jetbrains/kotlin/konan/blackboxtest/util/PackageNames.kt
@@ -15,7 +15,11 @@ import kotlin.math.min
 
 internal fun computePackageName(testDataBaseDir: File, testDataFile: File): PackageName {
     assertTrue(testDataFile.startsWith(testDataBaseDir)) {
-        "The file is outside of the directory.\nFile: $testDataFile\nDirectory: $testDataBaseDir"
+        """
+            The file is outside of the directory.
+            File: $testDataFile
+            Directory: $testDataBaseDir
+        """.trimIndent()
     }
 
     return testDataFile.parentFile