Fix integration test app detection

See gh-18631

Author: philwebb

spring-boot-tests/spring-boot-integration-tests/spring-boot-launch-script-tests/src/intTest/java/org/springframework/boot/launchscript/AbstractLaunchScriptIntegrationTests.java

@@ -30,6 +30,7 @@
 import org.testcontainers.utility.MountableFile;
 
 import org.springframework.boot.ansi.AnsiColor;
+import org.springframework.util.Assert;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.hamcrest.Matchers.containsString;
@@ -110,12 +111,10 @@ private LaunchScriptTestContainer(String os, String version, String scriptsDir,
 		}
 
 		private static File findApplication() {
-			File appJar = new File("build/app/build/libs/app.jar");
-			if (appJar.isFile()) {
-				return appJar;
-			}
-			throw new IllegalStateException(
-					"Could not find test application in build/app/build/libs directory. Have you built it?");
+			String name = String.format("build/%1$s/build/libs/%1$s.jar", "spring-boot-launch-script-tests-app");
+			File jar = new File(name);
+			Assert.state(jar.isFile(), () -> "Could not find " + name + ". Have you built it?");
+			return jar;
 		}
 
 	}

spring-boot-tests/spring-boot-integration-tests/spring-boot-loader-tests/src/intTest/java/org/springframework/boot/loader/LoaderIntegrationTests.java

@@ -28,6 +28,8 @@
 import org.testcontainers.utility.DockerImageName;
 import org.testcontainers.utility.MountableFile;
 
+import org.springframework.util.Assert;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -49,12 +51,10 @@ class LoaderIntegrationTests {
 			.withCommand("java", "-jar", "app.jar");
 
 	private static File findApplication() {
-		File appJar = new File("build/app/build/libs/app.jar");
-		if (appJar.isFile()) {
-			return appJar;
-		}
-		throw new IllegalStateException(
-				"Could not find test application in build/app/build/libs directory. Have you built it?");
+		String name = String.format("build/%1$s/build/libs/%1$s.jar", "spring-boot-loader-tests-app");
+		File jar = new File(name);
+		Assert.state(jar.isFile(), () -> "Could not find " + name + ". Have you built it?");
+		return jar;
 	}
 
 	@Test