For #16376: test view hierarchy depth in StartupExcessive*Test.

app/src/androidTest/java/org/mozilla/fenix/ui/StartupExcessiveResourceUseTest.kt

@@ -4,8 +4,13 @@
 
 package org.mozilla.fenix.ui
 
+import android.util.Log
+import android.view.View
+import android.view.ViewGroup
+import androidx.core.view.children
 import androidx.test.platform.app.InstrumentationRegistry
 import androidx.test.uiautomator.UiDevice
+import kotlinx.android.synthetic.main.activity_home.*
 import org.junit.Assert.assertEquals
 import org.junit.Rule
 import org.junit.Test
@@ -18,6 +23,7 @@ import org.mozilla.fenix.perf.ComponentInitCount
 private const val EXPECTED_SUPPRESSION_COUNT = 11
 private const val EXPECTED_RUNBLOCKING_COUNT = 2
 private const val EXPECTED_COMPONENT_INIT_COUNT = 42
+private const val EXPECTED_VIEW_HIERARCHY_DEPTH = 12
 
 private val failureMsgStrictMode = getErrorMessage(
     shortName = "StrictMode suppression",
@@ -34,6 +40,12 @@ private val failureMsgComponentInit = getErrorMessage(
     implications = "initializing new components on start up may be an indication that we're doing more work than necessary on start up?"
 )
 
+private val failureMsgViewHierarchyDepth = getErrorMessage(
+    shortName = "view hierarchy depth",
+    implications = "having a deep view hierarchy can slow down measure/layout performance?"
+) + "Please note that we're not sure if this is a useful metric to assert: with your feedback, " +
+    "we'll find out over time if it is or is not."
+
 /**
  * A performance test to limit the number of StrictMode suppressions and number of runBlocking used
  * on startup.
@@ -67,10 +79,25 @@ class StartupExcessiveResourceUseTest {
         val actualSuppresionCount = activityTestRule.activity.components.strictMode.suppressionCount.get().toInt()
         val actualRunBlocking = RunBlockingCounter.count.get()
         val actualComponentInitCount = ComponentInitCount.count.get()
+        val actualViewHierarchyDepth = countAndLogViewHierarchyDepth(activityTestRule.activity.rootContainer, 1)
 
         assertEquals(failureMsgStrictMode, EXPECTED_SUPPRESSION_COUNT, actualSuppresionCount)
         assertEquals(failureMsgRunBlocking, EXPECTED_RUNBLOCKING_COUNT, actualRunBlocking)
         assertEquals(failureMsgComponentInit, EXPECTED_COMPONENT_INIT_COUNT, actualComponentInitCount)
+        assertEquals(failureMsgViewHierarchyDepth, EXPECTED_VIEW_HIERARCHY_DEPTH, actualViewHierarchyDepth)
+    }
+}
+
+private fun countAndLogViewHierarchyDepth(view: View, level: Int): Int {
+    // Log for debugging purposes: not sure if this is actually helpful.
+    val indent = "| ".repeat(level - 1)
+    Log.d("Startup...Test", "${indent}$view")
+
+    return if (view !is ViewGroup) {
+        level
+    } else {
+        val maxDepth = view.children.map { countAndLogViewHierarchyDepth(it, level + 1) }.maxOrNull()
+        maxDepth ?: level
     }
 }