Hide the quick-switch button below two views (#150)

The pill only appears with something to switch between, so one enabled view
hides it just like zero. The floor that blocked disabling is gone from both
the settings screen and the view model.

app/src/test/java/de/jeanlucmakiola/calendula/ui/common/ViewBackStackTest.kt

@@ -120,4 +120,30 @@ class ViewBackStackTest {
         )
         assertThat(config.cycle).containsExactly(CalendarView.Agenda, CalendarView.Month).inOrder()
     }
+
+    @Test
+    fun `a cycle can be emptied down to no views at all`() {
+        // #150: the settings screen no longer holds a floor, so every view may go.
+        val config = QuickSwitchConfig(order = IMPLEMENTED_VIEWS, enabled = emptySet())
+        assertThat(config.cycle).isEmpty()
+        assertThat(config.cycle.size).isLessThan(QuickSwitchConfig.MIN_CYCLE)
+    }
+
+    @Test
+    fun `one enabled view is below the cycle minimum, so the pill hides`() {
+        // A single target is not a switch — it hides rather than becoming a
+        // jump-to-one-view button, which would be dead once you were there.
+        val config = QuickSwitchConfig(order = IMPLEMENTED_VIEWS, enabled = setOf(CalendarView.Day))
+        assertThat(config.cycle).containsExactly(CalendarView.Day)
+        assertThat(config.cycle.size).isLessThan(QuickSwitchConfig.MIN_CYCLE)
+    }
+
+    @Test
+    fun `two enabled views are enough to show the pill`() {
+        val config = QuickSwitchConfig(
+            order = IMPLEMENTED_VIEWS,
+            enabled = setOf(CalendarView.Day, CalendarView.Month),
+        )
+        assertThat(config.cycle.size).isAtLeast(QuickSwitchConfig.MIN_CYCLE)
+    }
 }