Test layout content changes

We were missing tests for items being removed from
Column, etc.

redwood-layout-composeui/src/androidUnitTest/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainerTest.kt

@@ -15,6 +15,7 @@
  */
 package app.cash.redwood.layout.composeui
 
+import app.cash.redwood.Modifier as RedwoodModifier
 import androidx.compose.foundation.background
 import androidx.compose.foundation.text.BasicText
 import androidx.compose.runtime.Composable
@@ -27,7 +28,6 @@ import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.unit.sp
 import app.cash.paparazzi.DeviceConfig
 import app.cash.paparazzi.Paparazzi
-import app.cash.redwood.Modifier as RedwoodModifier
 import app.cash.redwood.layout.AbstractFlexContainerTest
 import app.cash.redwood.layout.TestFlexContainer
 import app.cash.redwood.layout.Text
@@ -90,7 +90,17 @@ class ComposeUiFlexContainerTest(
     )
 
     override fun add(widget: Widget<@Composable () -> Unit>) {
-      delegate.children.insert(childCount++, widget)
+      addAt(childCount, widget)
+    }
+
+    override fun addAt(index: Int, widget: Widget<() -> Unit>) {
+      delegate.children.insert(index, widget)
+      childCount++
+    }
+
+    override fun removeAt(index: Int) {
+      delegate.children.remove(index = index, count = 1)
+      childCount--
     }
 
     override fun onEndChanges() {

redwood-layout-shared-test/src/commonMain/kotlin/app/cash/redwood/layout/AbstractFlexContainerTest.kt

@@ -415,6 +415,28 @@ abstract class AbstractFlexContainerTest<T : Any> {
     verifySnapshot(column)
   }
 
+  @Test
+  fun testDynamicElementUpdates() {
+    val container = flexContainer(FlexDirection.Column)
+    container.width(Constraint.Fill)
+    container.height(Constraint.Fill)
+    container.add(widget("A"))
+    container.add(widget("B"))
+    container.add(widget("D"))
+    container.add(widget("E"))
+
+    container.onEndChanges()
+    verifySnapshot(container, "ABDE")
+
+    container.addAt(index = 2, widget = widget("C"))
+    container.onEndChanges()
+    verifySnapshot(container, "ABCDE")
+
+    container.removeAt(index = 0)
+    container.onEndChanges()
+    verifySnapshot(container, "BCDE")
+  }
+
   /** We don't have assume() on kotlin.test. Tests that fail here should be skipped instead. */
   private fun assumeTrue(b: Boolean) {
     assertTrue(b)
@@ -429,6 +451,8 @@ interface TestFlexContainer<T : Any> : Widget<T>, ChangeListener {
   fun mainAxisAlignment(mainAxisAlignment: MainAxisAlignment)
   fun margin(margin: Margin)
   fun add(widget: Widget<T>)
+  fun addAt(index: Int, widget: Widget<T>)
+  fun removeAt(index: Int)
 }
 
 interface Text<T : Any> : Widget<T> {

redwood-layout-uiview/src/commonTest/kotlin/app/cash/redwood/layout/uiview/UIViewFlexContainerTest.kt

@@ -61,7 +61,17 @@ class UIViewFlexContainerTest(
     }
 
     override fun add(widget: Widget<UIView>) {
-      delegate.children.insert(childCount++, widget)
+      addAt(childCount, widget)
+    }
+
+    override fun addAt(index: Int, widget: Widget<UIView>) {
+      delegate.children.insert(index, widget)
+      childCount++
+    }
+
+    override fun removeAt(index: Int) {
+      delegate.children.remove(index = index, count = 1)
+      childCount--
     }
   }
 

redwood-layout-view/src/test/kotlin/app/cash/redwood/layout/view/ViewFlexContainerTest.kt

@@ -83,7 +83,17 @@ class ViewFlexContainerTest(
     )
 
     override fun add(widget: Widget<View>) {
-      delegate.children.insert(childCount++, widget)
+      addAt(childCount, widget)
+    }
+
+    override fun addAt(index: Int, widget: Widget<View>) {
+      delegate.children.insert(index, widget)
+      childCount++
+    }
+
+    override fun removeAt(index: Int) {
+      delegate.children.remove(index = index, count = 1)
+      childCount--
     }
   }
 }

redwood-lazylayout-composeui/src/androidUnitTest/kotlin/app/cash/redwood/layout/composeui/ComposeUiLazyListTest.kt

@@ -15,6 +15,7 @@
  */
 package app.cash.redwood.layout.composeui
 
+import app.cash.redwood.Modifier as RedwoodModifier
 import androidx.compose.foundation.background
 import androidx.compose.foundation.text.BasicText
 import androidx.compose.runtime.Composable
@@ -27,7 +28,6 @@ import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.unit.sp
 import app.cash.paparazzi.DeviceConfig
 import app.cash.paparazzi.Paparazzi
-import app.cash.redwood.Modifier as RedwoodModifier
 import app.cash.redwood.layout.AbstractFlexContainerTest
 import app.cash.redwood.layout.TestFlexContainer
 import app.cash.redwood.layout.Text
@@ -96,7 +96,17 @@ class ComposeUiLazyListTest(
     }
 
     override fun add(widget: Widget<@Composable () -> Unit>) {
-      delegate.items.insert(childCount++, widget)
+      addAt(childCount, widget)
+    }
+
+    override fun addAt(index: Int, widget: Widget<() -> Unit>) {
+      delegate.items.insert(index, widget)
+      childCount++
+    }
+
+    override fun removeAt(index: Int) {
+      delegate.items.remove(index = index, count = 1)
+      childCount--
     }
 
     override fun onEndChanges() {

redwood-lazylayout-view/src/test/kotlin/app/cash/redwood/lazylayout/view/ViewLazyListTest.kt

@@ -85,7 +85,17 @@ class ViewLazyListTest(
     }
 
     override fun add(widget: Widget<View>) {
-      delegate.items.insert(childCount++, widget)
+      addAt(childCount, widget)
+    }
+
+    override fun addAt(index: Int, widget: Widget<View>) {
+      delegate.items.insert(index, widget)
+      childCount++
+    }
+
+    override fun removeAt(index: Int) {
+      delegate.items.remove(index = index, count = 1)
+      childCount--
     }
   }
 }