Screenshot based testing

.run/test.run.xml

+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="test" type="GradleRunConfiguration" factoryName="Gradle">
+    <ExternalSystemSettings>
+      <option name="executionName" />
+      <option name="externalProjectPath" value="$PROJECT_DIR$/samples/SkijaInjectSample" />
+      <option name="externalSystemIdString" value="GRADLE" />
+      <option name="scriptParameters" value="" />
+      <option name="taskDescriptions">
+        <list />
+      </option>
+      <option name="taskNames">
+        <list>
+          <option value="test" />
+        </list>
+      </option>
+      <option name="vmOptions" value="" />
+    </ExternalSystemSettings>
+    <ExternalSystemDebugServerProcess>true</ExternalSystemDebugServerProcess>
+    <ExternalSystemReattachDebugProcess>true</ExternalSystemReattachDebugProcess>
+    <DebugAllEnabled>false</DebugAllEnabled>
+    <method v="2">
+      <option name="Gradle.BeforeRunTask" enabled="false" tasks="publishToMavenLocal" externalProjectPath="$PROJECT_DIR$/skiko" vmOptions="" scriptParameters="" />
+    </method>
+  </configuration>
+</component>
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samples/SkijaInjectSample/build.gradle

@@ -56,4 +56,15 @@ application {
 
 run {
     systemProperty("skiko.fps.enabled", "true")
+}
+
+test {
+    systemProperty("skiko.test.screenshots.dir", new File(project.projectDir, "src/test/screenshots").absolutePath)
+
+    // Tests should be determined, so disable scaling.
+    // On MacOs we need the actual scale, otherwise we will have aliased screenshots because of scaling.
+    if (System.getProperty("os.name") != "Mac OS X") {
+        systemProperty("sun.java2d.dpiaware", "false")
+        systemProperty("sun.java2d.uiScale", "1")
+    }
 }
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samples/SkijaInjectSample/src/test/kotlin/SkijaInjectSample/AppTest.kt

-/*
- * This Kotlin source file was generated by the Gradle 'init' task.
- */
-package SkijaInjectSample
-
-import kotlin.test.Test
-import kotlin.test.assertNotNull
-
-class AppTest {
-    // @Test fun testAppHasAGreeting() {
-    //     val classUnderTest = App()
-    //     assertNotNull(classUnderTest.greeting, "app should have a greeting")
-    // }
-}

samples/SkijaInjectSample/src/test/kotlin/org/jetbrains/skiko/Images.kt

+package org.jetbrains.skiko
+
+import java.awt.image.BufferedImage
+
+fun isContentSame(img1: BufferedImage, img2: BufferedImage): Boolean {
+    if (img1.width == img2.width && img1.height == img2.height) {
+        for (x in 0 until img1.width) {
+            for (y in 0 until img1.height) {
+                if (img1.getRGB(x, y) != img2.getRGB(x, y)) {
+                    return false
+                }
+            }
+        }
+    } else {
+        return false
+    }
+    return true
+}
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samples/SkijaInjectSample/src/test/kotlin/org/jetbrains/skiko/ScreenshotTestRule.kt

+package org.jetbrains.skiko
+
+import org.junit.rules.TestRule
+import org.junit.runner.Description
+import org.junit.runners.model.Statement
+import java.awt.Rectangle
+import java.awt.Robot
+import java.io.File
+import javax.imageio.ImageIO
+
+// TODO macOs has wrong colors. Only white, black, red and green are correct
+class ScreenshotTestRule(private val robot: Robot) : TestRule {
+    private lateinit var testIdentifier: String
+    private val screenshotsDir = File(System.getProperty("skiko.test.screenshots.dir")!!)
+
+    override fun apply(base: Statement, description: Description): Statement {
+        return object : Statement() {
+            override fun evaluate() {
+                testIdentifier = "${description.className}_${description.methodName}"
+                    .replace(".", "_")
+                    .replace(",", "_")
+                    .replace(" ", "_")
+                    .replace("(", "_")
+                    .replace(")", "_")
+                    .replace("__", "_")
+                    .replace("__", "_")
+                    .removePrefix("_")
+                    .removeSuffix("_")
+                base.evaluate()
+            }
+        }
+    }
+
+    fun assert(rectangle: Rectangle, id: String = "") {
+        val actual = robot.createScreenCapture(rectangle)
+        val name = if (id.isNotEmpty()) "${testIdentifier}_$id" else testIdentifier
+        val actualFile = File(screenshotsDir, "${name}_actual.png")
+        val expectedFile = File(screenshotsDir, "$name.png")
+        if (actualFile.exists()) {
+            actualFile.delete()
+        }
+        if (expectedFile.exists()) {
+            val expected = ImageIO.read(expectedFile)
+            if (!isContentSame(expected, actual)) {
+                ImageIO.write(actual, "png", actualFile)
+                throw AssertionError(
+                    "Image mismatch! Expected image ${expectedFile.absolutePath}, actual: ${actualFile.absolutePath}"
+                )
+            }
+        } else {
+            ImageIO.write(actual, "png", actualFile)
+            throw AssertionError(
+                "Missing screenshot image " +
+                        "${actualFile.absolutePath}. " +
+                        "Did you mean to check in a new image?"
+            )
+        }
+    }
+}
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