Disable tests that use Docker when Docker is unavailable

Closes gh-19616

spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/testcontainers/DisabledIfDockerUnavailable.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.boot.testsupport.testcontainers;
+
+import org.junit.jupiter.api.extension.ConditionEvaluationResult;
+import org.junit.jupiter.api.extension.ExecutionCondition;
+import org.junit.jupiter.api.extension.ExtensionContext;
+import org.testcontainers.DockerClientFactory;
+
+/**
+ * An {@link ExecutionCondition} that disables execution if Docker is unavailable.
+ *
+ * @author Andy Wilkinson
+ */
+public class DisabledIfDockerUnavailable implements ExecutionCondition {
+
+	@Override
+	public ConditionEvaluationResult evaluateExecutionCondition(ExtensionContext context) {
+		System.out.println("Checking Docker's availability");
+		if (isDockerAvailable()) {
+			System.out.println("Docker available");
+			return ConditionEvaluationResult.enabled("Docker is available");
+		}
+		System.out.println("Docker unavailable");
+		return ConditionEvaluationResult.disabled("Docker is not available");
+	}
+
+	private boolean isDockerAvailable() {
+		try {
+			DockerClientFactory.instance().client();
+			return true;
+		}
+		catch (Throwable ex) {
+			return false;
+		}
+	}
+
+}