Only enable flaky test support on CI

Closes gh-21272

Author: wilkinsona

buildSrc/src/main/java/org/springframework/boot/build/JavaConventions.java

@@ -107,17 +107,19 @@ private void configureJarManifestConventions(Project project) {
 	}
 
 	private void configureTestConventions(Project project) {
-		project.getPlugins().apply(TestRetryPlugin.class);
-		project.getTasks().withType(Test.class, (test) -> {
-			withOptionalBuildJavaHome(project, (javaHome) -> test.setExecutable(javaHome + "/bin/java"));
-			test.useJUnitPlatform();
-			test.setMaxHeapSize("1024M");
-			project.getPlugins().withType(TestRetryPlugin.class, (testRetryPlugin) -> {
-				TestRetryTaskExtension testRetry = test.getExtensions().getByType(TestRetryTaskExtension.class);
-				testRetry.getFailOnPassedAfterRetry().set(true);
-				testRetry.getMaxRetries().set(3);
+		if (Boolean.valueOf(System.getenv("CI"))) {
+			project.getPlugins().apply(TestRetryPlugin.class);
+			project.getTasks().withType(Test.class, (test) -> {
+				withOptionalBuildJavaHome(project, (javaHome) -> test.setExecutable(javaHome + "/bin/java"));
+				test.useJUnitPlatform();
+				test.setMaxHeapSize("1024M");
+				project.getPlugins().withType(TestRetryPlugin.class, (testRetryPlugin) -> {
+					TestRetryTaskExtension testRetry = test.getExtensions().getByType(TestRetryTaskExtension.class);
+					testRetry.getFailOnPassedAfterRetry().set(true);
+					testRetry.getMaxRetries().set(3);
+				});
 			});
-		});
+		}
 	}
 
 	private void configureJavadocConventions(Project project) {

buildSrc/src/test/java/org/springframework/boot/build/ConventionsPluginTests.java

@@ -21,6 +21,8 @@
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.PrintWriter;
+import java.util.Collections;
+import java.util.Map;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
@@ -76,7 +78,7 @@ void jarIncludesLegalFiles() throws IOException {
 	}
 
 	@Test
-	void testRetryIsConfigured() throws IOException {
+	void testRetryIsConfiguredOnCI() throws IOException {
 		try (PrintWriter out = new PrintWriter(new FileWriter(this.buildFile))) {
 			out.println("plugins {");
 			out.println("    id 'java'");
@@ -85,19 +87,44 @@ void testRetryIsConfigured() throws IOException {
 			out.println("description 'Test'");
 			out.println("task retryConfig {");
 			out.println("    doLast {");
+			out.println("        println \"Retry plugin applied: ${plugins.hasPlugin('org.gradle.test-retry')}\"");
 			out.println("    test.retry {");
 			out.println("            println \"maxRetries: ${maxRetries.get()}\"");
 			out.println("            println \"failOnPassedAfterRetry: ${failOnPassedAfterRetry.get()}\"");
 			out.println("        }");
 			out.println("    }");
 			out.println("}");
 		}
-		assertThat(runGradle("retryConfig", "--stacktrace").getOutput()).contains("maxRetries: 3")
+		assertThat(runGradle(Collections.singletonMap("CI", "true"), "retryConfig", "--stacktrace").getOutput())
+				.contains("Retry plugin applied: true").contains("maxRetries: 3")
 				.contains("failOnPassedAfterRetry: true");
 	}
 
+	@Test
+	void testRetryIsNotConfiguredLocally() throws IOException {
+		try (PrintWriter out = new PrintWriter(new FileWriter(this.buildFile))) {
+			out.println("plugins {");
+			out.println("    id 'java'");
+			out.println("    id 'org.springframework.boot.conventions'");
+			out.println("}");
+			out.println("description 'Test'");
+			out.println("task retryConfig {");
+			out.println("    doLast {");
+			out.println("        println \"Retry plugin applied: ${plugins.hasPlugin('org.gradle.test-retry')}\"");
+			out.println("    }");
+			out.println("}");
+		}
+		assertThat(runGradle(Collections.singletonMap("CI", "local"), "retryConfig", "--stacktrace").getOutput())
+				.contains("Retry plugin applied: false");
+	}
+
 	private BuildResult runGradle(String... args) {
-		return GradleRunner.create().withProjectDir(this.projectDir).withArguments(args).withPluginClasspath().build();
+		return runGradle(Collections.emptyMap(), args);
+	}
+
+	private BuildResult runGradle(Map<String, String> environment, String... args) {
+		return GradleRunner.create().withProjectDir(this.projectDir).withEnvironment(environment).withArguments(args)
+				.withPluginClasspath().build();
 	}
 
 }