adds unit test for PetOwner_bookVisit

... defaulting of param #1
diff --git a/module-visit/src/test/java/domainapp/modules/visit/contributions/PetOwner_bookVisit_Test.java b/module-visit/src/test/java/domainapp/modules/visit/contributions/PetOwner_bookVisit_Test.java
new file mode 100644
index 0000000..3f69da9
--- /dev/null
+++ b/module-visit/src/test/java/domainapp/modules/visit/contributions/PetOwner_bookVisit_Test.java
@@ -0,0 +1,51 @@
+package domainapp.modules.visit.contributions;
+
+import java.time.LocalDateTime;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import org.apache.causeway.applib.clock.VirtualClock;
+import org.apache.causeway.applib.services.clock.ClockService;
+
+@ExtendWith(MockitoExtension.class)
+public class PetOwner_bookVisit_Test {
+
+    @Mock ClockService mockClockService;
+    @Mock VirtualClock mockVirtualClock;
+
+    @BeforeEach
+    void setup() {
+        Mockito.when(mockClockService.getClock()).thenReturn(mockVirtualClock); // <.>
+    }
+
+    @Nested
+    class default1 {
+
+        @Test
+        void defaults_to_9am_tomorrow_morning() {
+
+            // given
+            PetOwner_bookVisit mixin = new PetOwner_bookVisit(null);
+            mixin.clockService = mockClockService;
+
+            LocalDateTime now = LocalDateTime.of(2024, 5, 26, 16, 37, 45);
+
+            // expecting
+            Mockito.when(mockVirtualClock.nowAsLocalDate()).thenReturn(now.toLocalDate());
+
+            // when
+            LocalDateTime localDateTime = mixin.default1Act();
+
+            // then
+            Assertions.assertThat(localDateTime)
+                    .isEqualTo(LocalDateTime.of(2024,5,27,9,0,0));
+        }
+    }
+}