From f37c6d151c607d6f0a197f44af42fe39726cf2f1 Mon Sep 17 00:00:00 2001
From: Peter Abbondanzo <abbo@meta.com>
Date: Thu, 22 Oct 2026 09:47:30 -0700
Subject: [PATCH] Add unit test for TextLayoutManager desired width
 optimization (#59202)

Summary:

Add a Robolectric test that verifies `Layout.getDesiredWidth` is only called when necessary during text layout.

The test confirms the optimization that avoids expensive width measurements for `EXACTLY` mode and for `AT_MOST` mode when boring text doesn't fit. It uses `mockStatic` to intercept calls to `Layout.getDesiredWidth` and verifies the correct number of invocations across different measure modes.

Changelog: [Internal]

Reviewed By: andrewdacenko

Differential Revision: D125868474
---
 .../text/TextLayoutManagerDesiredWidthTest.kt | 114 ++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/text/TextLayoutManagerDesiredWidthTest.kt

diff --git a/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/text/TextLayoutManagerDesiredWidthTest.kt b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/text/TextLayoutManagerDesiredWidthTest.kt
new file mode 100644
index 00000000000..dcb4b213ee8
--- /dev/null
+++ b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/text/TextLayoutManagerDesiredWidthTest.kt
@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.views.text
+
+import android.annotation.SuppressLint
+import android.graphics.text.LineBreakConfig
+import android.text.BoringLayout
+import android.text.Layout
+import android.text.SpannableString
+import android.text.TextPaint
+import com.facebook.yoga.YogaMeasureMode
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.MockedStatic
+import org.mockito.Mockito.CALLS_REAL_METHODS
+import org.mockito.Mockito.mockStatic
+import org.mockito.Mockito.never
+import org.mockito.Mockito.times
+import org.mockito.kotlin.any
+import org.mockito.verification.VerificationMode
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+@RunWith(RobolectricTestRunner::class)
+@SuppressLint("NewApi")
+@Config(sdk = [35])
+class TextLayoutManagerDesiredWidthTest {
+
+  @Test
+  fun `EXACTLY mode does not measure the desired width`() {
+    mockStatic(Layout::class.java, CALLS_REAL_METHODS).use { layoutStatic ->
+      val layout = createLayout(YogaMeasureMode.EXACTLY, boring = null)
+
+      layoutStatic.verifyDesiredWidthCalls(never())
+      assertThat(layout.width).isEqualTo(LAYOUT_WIDTH.toInt())
+    }
+  }
+
+  @Test
+  fun `AT_MOST mode does not measure the desired width when boring text does not fit`() {
+    mockStatic(Layout::class.java, CALLS_REAL_METHODS).use { layoutStatic ->
+      val layout = createLayout(YogaMeasureMode.AT_MOST, boring = boringMetrics(width = 500))
+
+      layoutStatic.verifyDesiredWidthCalls(never())
+      assertThat(layout.width).isEqualTo(LAYOUT_WIDTH.toInt())
+    }
+  }
+
+  @Test
+  fun `AT_MOST mode measures the desired width when the text is not boring`() {
+    mockStatic(Layout::class.java, CALLS_REAL_METHODS).use { layoutStatic ->
+      val layout = createLayout(YogaMeasureMode.AT_MOST, boring = null)
+
+      layoutStatic.verifyDesiredWidthCalls(times(1))
+      assertThat(layout.width).isLessThanOrEqualTo(LAYOUT_WIDTH.toInt())
+    }
+  }
+
+  @Test
+  fun `UNDEFINED mode measures the desired width when the text is not boring`() {
+    mockStatic(Layout::class.java, CALLS_REAL_METHODS).use { layoutStatic ->
+      val layout = createLayout(YogaMeasureMode.UNDEFINED, boring = null)
+
+      layoutStatic.verifyDesiredWidthCalls(times(1))
+      assertThat(layout.lineCount).isEqualTo(1)
+    }
+  }
+
+  private fun MockedStatic<Layout>.verifyDesiredWidthCalls(mode: VerificationMode) {
+    verify({ Layout.getDesiredWidth(any<CharSequence>(), any<TextPaint>()) }, mode)
+  }
+
+  private fun boringMetrics(width: Int): BoringLayout.Metrics =
+      BoringLayout.Metrics().apply {
+        this.width = width
+        ascent = -20
+        descent = 5
+        top = -22
+        bottom = 6
+      }
+
+  private fun createLayout(
+      widthMode: YogaMeasureMode,
+      boring: BoringLayout.Metrics?,
+      lineBreakStyle: Int = LineBreakConfig.LINE_BREAK_STYLE_NONE,
+      lineBreakWordStyle: Int = LineBreakConfig.LINE_BREAK_WORD_STYLE_NONE,
+  ): Layout =
+      TextLayoutManager.createLayout(
+          text = SpannableString("hello world"),
+          boring = boring,
+          width = LAYOUT_WIDTH,
+          widthYogaMeasureMode = widthMode,
+          includeFontPadding = false,
+          textBreakStrategy = Layout.BREAK_STRATEGY_HIGH_QUALITY,
+          hyphenationFrequency = Layout.HYPHENATION_FREQUENCY_NONE,
+          lineBreakStyle = lineBreakStyle,
+          lineBreakWordStyle = lineBreakWordStyle,
+          alignment = Layout.Alignment.ALIGN_NORMAL,
+          justificationMode = 0,
+          ellipsizeMode = null,
+          maxNumberOfLines = 2,
+          paint = TextPaint(TextPaint.ANTI_ALIAS_FLAG).apply { textSize = 26f },
+      )
+
+  private companion object {
+    const val LAYOUT_WIDTH = 200f
+  }
+}