scrollbar test, match test to expected behavior

src/app.rs

@@ -332,7 +332,7 @@ impl App {
                         i - 1
                     }
                 }
-                None => 0,
+                None => return,  // do nothing if table_state == None && previous_program() called
             };
             self.table_state.select(Some(i));
             self.vertical_scroll_state = self.vertical_scroll_state.position(self.vertical_scroll);
@@ -483,18 +483,23 @@ mod tests {
 
         // Initially no item is selected
         assert_eq!(app.selected_program(), None, "expected no program");
+        assert_eq!(app.vertical_scroll, 0, "expected init with 0, got: {}", app.vertical_scroll);
 
         // After calling next, the first item should be selected
         app.next_program();
         assert_eq!(app.selected_program(), Some(prog_1.clone()), "expected prog_1");
+        assert_eq!(app.vertical_scroll, 0, "expected scroll 0, got: {}", app.vertical_scroll);
 
         // After calling next again, the second item should be selected
         app.next_program();
         assert_eq!(app.selected_program(), Some(prog_2.clone()), "expected prog_2");
+        assert_eq!(app.vertical_scroll, 1, "expected scroll 1, got: {}", app.vertical_scroll);
 
-        // After calling next again, we should wrap around to the first item
+        // After calling next again, the second item should still be selected without wrapping
         app.next_program();
         assert_eq!(app.selected_program(), Some(prog_2.clone()), "expected prog_2; no wrap around");
+        assert_eq!(app.vertical_scroll, 1, "expected scroll 1, got: {}", app.vertical_scroll);
+
     }
 
     #[test]
@@ -503,10 +508,17 @@ mod tests {
 
         // Initially no item is selected
         assert_eq!(app.selected_program(), None);
+
+        // Initially ScrollbarState is 0
+        assert_eq!(app.vertical_scroll_state, ScrollbarState::new(0), "unexpected ScrollbarState");
+        assert_eq!(app.vertical_scroll, 0, "expected 0 vertical_scroll, got: {}", app.vertical_scroll);
 
         // After calling previous, no item should be selected
         app.previous_program();
         assert_eq!(app.selected_program(), None);
+
+        assert_eq!(app.vertical_scroll_state, ScrollbarState::new(0), "unexpected ScrollbarState");
+        assert_eq!(app.vertical_scroll, 0, "expected 0 vertical_scroll, got: {}", app.vertical_scroll);
     }
 
     #[test]
@@ -544,18 +556,26 @@ mod tests {
 
         // Initially no item is selected
         assert_eq!(app.selected_program(), None, "expected no program");
+        assert_eq!(app.vertical_scroll, 0, "expected init with 0");
 
-        // After calling previous, the last item should be selected
+        // After calling previous with no table state, nothing should be selected
         app.previous_program();
-        assert_eq!(app.selected_program(), Some(prog_1.clone()), "expected prog_1");
+        assert_eq!(app.selected_program(), None, "expected None");
+        assert_eq!(app.vertical_scroll, 0, "still 0, no wrapping");
 
-        // After calling previous again, the first item should be selected
+        // After calling previous again, still nothing should be selected
         app.previous_program();
-        assert_eq!(app.selected_program(), Some(prog_1.clone()), "still prog_1");
+        assert_eq!(app.selected_program(), None, "still None");
+        assert_eq!(app.vertical_scroll, 0, "still 0, no wrapping");
+
+        app.next_program();  // populate table state and expect prog_1 selected
+        assert_eq!(app.selected_program(), Some(prog_1.clone()), "expected prog_1");
+        assert_eq!(app.vertical_scroll, 0, "expected scroll 0");
 
-        // After calling previous again, we should wrap around to the last item
+        // After calling previous again, prog_1 should still be selected (0th index)
         app.previous_program();
         assert_eq!(app.selected_program(), Some(prog_1.clone()), "still expecting prog_1");
+        assert_eq!(app.vertical_scroll, 0, "still 0, no wrapping");
     }
 
     #[test]