Add test to check no real constructor is called

This test would fail without the changes from the previous commit.

src/test/java/com/diffblue/deeptestutils/regression/ClassWithConstructor.java

@@ -0,0 +1,12 @@
+package com.diffblue.deeptestutils.regression;
+
+public class ClassWithConstructor {
+
+  public static Integer integerField;
+
+  public int intField;
+
+  public ClassWithConstructor() {
+    intField = integerField.intValue();
+  }
+}

src/test/java/com/diffblue/deeptestutils/regression/ReflectorGetInstanceTest.java

@@ -0,0 +1,20 @@
+package com.diffblue.deeptestutils.regression;
+
+import org.junit.Assert;
+import org.junit.Test;
+import java.lang.reflect.InvocationTargetException;
+import com.diffblue.deeptestutils.Reflector;
+
+public class ReflectorGetInstanceTest {
+
+  // This test checks that in a class with a constructor with no arguments,
+  // calling Reflector.getInstance does not cause a call to that constructor.
+  // If the constructor was called, a NullPointerException would happen as
+  // integerField has its default value of null.
+  @Test
+  public void checkNoConstructorCall() throws InvocationTargetException {
+    ClassWithConstructor cwc = (ClassWithConstructor) Reflector.getInstance
+        ("com.diffblue.deeptestutils.regression.ClassWithConstructor");
+    Assert.assertEquals(cwc.intField, 0);
+  }
+}