Added test for getting all tutors when no tutors exist.

backend/src/test/kotlin/uk/co/neviyn/observationdatabase/ControllerTest.kt

@@ -71,6 +71,12 @@ class ControllerTest {
         assertTrue(result.contains(NameValue("Bar", 2)))
     }
 
+    @Test
+    fun testGetAllTutors_NoTutors(){
+        val result = controller.getAllTutors()
+        assertTrue(result.isEmpty())
+    }
+
     @Test
     fun testAddTutor() {
         val site = Site(1, "X")