diff --git a/metafacture-io/src/test/java/org/metafacture/io/HttpOpenerTest.java b/metafacture-io/src/test/java/org/metafacture/io/HttpOpenerTest.java
index 87dcdda39..dd3bdbb1a 100644
--- a/metafacture-io/src/test/java/org/metafacture/io/HttpOpenerTest.java
+++ b/metafacture-io/src/test/java/org/metafacture/io/HttpOpenerTest.java
@@ -330,16 +330,14 @@ private void shouldPerformRequest(final String input, final HttpOpener.Method me
 
         WireMock.stubFor(stub);
 
-        TestHelpers.assertReader(receiver, responseBody, () -> {
+        TestHelpers.assertReader(receiver, () -> {
             opener.process(String.format(input, baseUrl));
 
             // use the opener a second time in a workflow:
             opener.process(String.format(input, baseUrl));
 
             opener.closeStream();
-
-            return 2;
-        });
+        }, responseBody, responseBody);
 
         WireMock.verify(request);
     }
diff --git a/metafacture-io/src/test/java/org/metafacture/io/TestHelpers.java b/metafacture-io/src/test/java/org/metafacture/io/TestHelpers.java
index bb4c7725e..722cefeb0 100644
--- a/metafacture-io/src/test/java/org/metafacture/io/TestHelpers.java
+++ b/metafacture-io/src/test/java/org/metafacture/io/TestHelpers.java
@@ -24,13 +24,15 @@
 
 import java.io.File;
 import java.io.Reader;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 import java.util.function.Consumer;
-import java.util.function.IntSupplier;
 
 public final class TestHelpers {
 
     public static void assertFile(final ObjectReceiver<Reader> receiver, final String expected, final File file, final Consumer<FileOpener> consumer) {
-        assertReader(receiver, expected, () -> {
+        assertReader(receiver, () -> {
             final FileOpener opener = new FileOpener();
             if (consumer != null) {
                 consumer.accept(opener);
@@ -39,25 +41,18 @@ public static void assertFile(final ObjectReceiver<Reader> receiver, final Strin
             opener.setReceiver(receiver);
             opener.process(file.getAbsolutePath());
             opener.closeStream();
-
-            return 1;
-        });
+        }, expected);
     }
 
-    public static void assertReader(final ObjectReceiver<Reader> receiver, final String expected, final IntSupplier supplier) {
-        final StringBuilder sb = new StringBuilder();
-
-        Mockito.doAnswer(i -> {
-            sb.delete(0, sb.length());
-            sb.append(ResourceUtil.readAll(i.getArgument(0)));
-
-            return null;
-        }).when(receiver).process(Mockito.any(Reader.class));
+    public static void assertReader(final ObjectReceiver<Reader> receiver, final Runnable runnable, final String... expected) {
+        final List<String> actual = new ArrayList<>();
+        Mockito.doAnswer(i -> actual.add(ResourceUtil.readAll(i.getArgument(0)))).when(receiver).process(Mockito.any(Reader.class));
 
-        final int times = supplier.getAsInt();
+        runnable.run();
 
-        Mockito.verify(receiver, Mockito.times(times)).process(Mockito.any(Reader.class));
-        Assert.assertEquals(expected, sb.toString());
+        Mockito.verify(receiver, Mockito.times(expected.length)).process(Mockito.any(Reader.class));
+        Arrays.stream(expected).forEach(i -> Assert.assertEquals(i, actual.remove(0)));
+        Assert.assertEquals(0, actual.size());
     }
 
 }