Added a test and extended CanSubclassCheckerTest in src/test/java/org/mutabilitydetector/benchmarks/CanSubclassCheckerTest.java b/src/test/java/org/mutabilitydetector/benchmarks/CanSubclassCheckerTest.java

CanSubclassCheckerTest.java

diff --git a/src/test/java/org/mutabilitydetector/benchmarks/CanSubclassCheckerTest.java b/src/test/java/org/mutabilitydetector/benchmarks/CanSubclassCheckerTest.java
index 988c019..bd99158 100644
--- a/src/test/java/org/mutabilitydetector/benchmarks/CanSubclassCheckerTest.java
+++ b/src/test/java/org/mutabilitydetector/benchmarks/CanSubclassCheckerTest.java
@@ -42,6 +42,7 @@ import org.mutabilitydetector.benchmarks.sealed.SealedImmutable;
 import org.mutabilitydetector.benchmarks.types.EnumType;
 import org.mutabilitydetector.checkers.CanSubclassChecker;
 import org.mutabilitydetector.locations.ClassLocation;
+import org.mutabilitydetector.unittesting.MutabilityAssert;
 
 @RunWith(Theories.class)
 public class CanSubclassCheckerTest {
@@ -59,6 +60,7 @@ public class CanSubclassCheckerTest {
         AnalysisResultTheory.of(HasFinalFieldsAndADefaultConstructor.class, NOT_IMMUTABLE),
         AnalysisResultTheory.of(IsFinalAndHasOnlyPrivateConstructors.class, IMMUTABLE),
         AnalysisResultTheory.of(ImmutableByHavingOnlyPrivateConstructors.class, IMMUTABLE),
+        AnalysisResultTheory.of(ImmutableByHavingOnlyAPrivateConstructorUsingTheBuilderPattern.class, IMMUTABLE),
     };
 
     @Theory
@@ -90,4 +92,8 @@ public class CanSubclassCheckerTest {
         assertThat(location.typeName(), is(MutableByNotBeingFinalClass.class.getName()));
     }
     
+    @Test
+    public void privateConstructorsUsingBuilderPatternAreImmutable() throws Exception {
+      MutabilityAssert.assertImmutable(ImmutableByHavingOnlyAPrivateConstructorUsingTheBuilderPattern.class);
+    }
 }