Add unit test for WebAssets class

include-build/roborazzi-gradle-plugin/build.gradle

@@ -25,6 +25,9 @@ dependencies {
   integrationTestDepImplementation libs.android.tools.build.gradle
   integrationTestDepImplementation libs.kotlin.gradle.plugin
   integrationTestDepImplementation libs.compose.gradle.plugin
+  testImplementation libs.kotlin.test
+  testImplementation libs.kotlin.test.junit
+  testImplementation libs.junit
 }
 
 sourceSets {

include-build/roborazzi-gradle-plugin/src/test/java/io/github/takahirom/roborazzi/WebAssetsTest.kt

@@ -0,0 +1,31 @@
+package io.github.takahirom.roborazzi
+
+import junit.framework.TestCase.assertTrue
+import org.junit.Rule
+import org.junit.rules.TemporaryFolder
+import java.io.File
+import kotlin.test.Test
+
+class WebAssetsTest {
+
+  @get:Rule
+  val tmpDir: TemporaryFolder = TemporaryFolder.builder().assureDeletion().build()
+
+  @Test
+  fun testWritesWebAssetsSuccessfullyToReportsDirectory() {
+    val reportDir = tmpDir.newFolder("roborazzi-reports")
+    val cssFile = File(reportDir, "assets/report-style.css")
+    val materializeCssFile = File(reportDir, "assets/materialize.min.css")
+    val materializeJsFile = File(reportDir, "assets/materialize.min.js")
+    val materialIconsCssFile = File(reportDir, "assets/material-icons.css")
+    val materialIconsTtfFile = File(reportDir, "assets/MaterialIcons-Regular.ttf")
+
+    WebAssets.create().writeToRoborazziReportsDir(reportDir)
+
+    assertTrue(cssFile.exists())
+    assertTrue(materializeCssFile.exists())
+    assertTrue(materializeJsFile.exists())
+    assertTrue(materialIconsCssFile.exists())
+    assertTrue(materialIconsTtfFile.exists())
+  }
+}