Add @LongRunningTest JUnit 5 condition

* Add docs about `@LongRunningTest`

spring-integration-test-support/src/main/java/org/springframework/integration/test/condition/LongRunningTest.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.test.condition;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.junit.jupiter.api.condition.EnabledIf;
+
+/**
+ * JUnit Jupiter condition to prevent long running tests from running on every build;
+ * set environment variable {@code RUN_LONG_INTEGRATION_TESTS} on a CI nightly build to ensure coverage.
+ *
+ * @author Artem Bilan
+ *
+ * @since 5.1
+ */
+@Target({ ElementType.TYPE, ElementType.METHOD })
+@Retention(RetentionPolicy.RUNTIME)
+@EnabledIf(LongRunningTest.LONG_RUNNING_SCRIPT)
+public @interface LongRunningTest {
+
+	String LONG_RUNNING_SCRIPT =
+			"systemEnvironment.get('RUN_LONG_INTEGRATION_TESTS') == 'true' ||" +
+					" systemProperty.get('RUN_LONG_INTEGRATION_TESTS') == 'true'";
+
+}