diff --git a/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java b/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java
index 5d5b5e022..eca359983 100644
--- a/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java
+++ b/processor/src/test/java/org/mapstruct/ap/testutil/MapperTestBase.java
@@ -73,7 +73,7 @@ public abstract class MapperTestBase {
     private String classOutputDir;
     private String sourceOutputDir;
     private List<File> classPath;
-    private List<String> libraries;
+    private final List<String> libraries;
     private DiagnosticCollector<JavaFileObject> diagnostics;
 
     public MapperTestBase() {
@@ -147,14 +147,18 @@ public abstract class MapperTestBase {
         Iterator<DiagnosticDescriptor> actualIterator = actualDiagnostics.iterator();
         Iterator<DiagnosticDescriptor> expectedIterator = expectedDiagnostics.iterator();
 
+        assertThat( actualDiagnostics ).describedAs(
+            String.format(
+                "Numbers of expected and actual diagnostics are diffent. Actual:%s%s%sExpected:%s%s.",
+                System.lineSeparator(),
+                actualDiagnostics.toString().replace( ", ", System.lineSeparator() ),
+                System.lineSeparator(),
+                System.lineSeparator(),
+                expectedDiagnostics.toString().replace( ", ", System.lineSeparator() )
+            )
+        ).hasSize( expectedDiagnostics.size() );
+
         while ( actualIterator.hasNext() ) {
-            assertThat( expectedIterator.hasNext() ).describedAs(
-                String.format(
-                    "Found more diagnostics than expected. Actual: %s; Expected: %s.",
-                    actualDiagnostics,
-                    expectedDiagnostics
-                )
-            ).isTrue();
 
             DiagnosticDescriptor actual = actualIterator.next();
             DiagnosticDescriptor expected = expectedIterator.next();
@@ -171,14 +175,6 @@ public abstract class MapperTestBase {
                 )
             ).matches( ".*" + expected.getMessage() + ".*" );
         }
-
-        assertThat( expectedIterator.hasNext() ).describedAs(
-            String.format(
-                "Found less diagnostics than expected. Actual: %s; Expected: %s.",
-                actualDiagnostics,
-                expectedDiagnostics
-            )
-        ).isFalse();
     }
 
     /**
diff --git a/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/DiagnosticDescriptor.java b/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/DiagnosticDescriptor.java
index 327e89993..a4a8c736d 100644
--- a/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/DiagnosticDescriptor.java
+++ b/processor/src/test/java/org/mapstruct/ap/testutil/compilation/model/DiagnosticDescriptor.java
@@ -167,8 +167,8 @@ public class DiagnosticDescriptor {
 
     @Override
     public String toString() {
-        return "DiagnosticDescriptor [sourceFileName=" + sourceFileName
-            + ", kind=" + kind + ", line=" + line + ", message=" + message
-            + "]";
+        String sourceFileName = this.sourceFileName
+            .substring( this.sourceFileName.lastIndexOf( File.separatorChar ) + 1 );
+        return "DiagnosticDescriptor: " + kind + " " + sourceFileName + ":" + line + " " + message;
     }
 }