Fix MutableDiagnosticsTest#testCaching()

Sadly relying on implementation details

compiler/frontend/src/org/jetbrains/jet/lang/resolve/DiagnosticsWithSuppression.java

@@ -26,6 +26,7 @@ import com.intellij.util.containers.ConcurrentWeakValueHashMap;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.containers.FilteringIterator;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.TestOnly;
 import org.jetbrains.jet.lang.descriptors.annotations.AnnotationDescriptor;
 import org.jetbrains.jet.lang.diagnostics.Diagnostic;
 import org.jetbrains.jet.lang.diagnostics.DiagnosticFactory;
@@ -298,4 +299,10 @@ public class DiagnosticsWithSuppression implements Diagnostics {
             return other instanceof EmptySuppressor;
         }
     }
+
+    @TestOnly
+    @NotNull
+    public Collection<Diagnostic> getDiagnostics() {
+        return diagnostics;
+    }
 }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/MutableDiagnosticsWithSuppression.kt

@@ -22,6 +22,7 @@ import com.intellij.openapi.util.CompositeModificationTracker
 import com.intellij.util.CachedValueImpl
 import com.intellij.psi.util.CachedValueProvider
 import com.intellij.psi.PsiElement
+import org.jetbrains.annotations.TestOnly
 
 public class MutableDiagnosticsWithSuppression(
         private val bindingContext: BindingContext,
@@ -56,4 +57,5 @@ public class MutableDiagnosticsWithSuppression(
         modificationTracker.incModificationCount()
     }
 
-}
+    TestOnly public fun getReadonlyView(): DiagnosticsWithSuppression = readonlyView()
+}