Fix potential @AutoConfigureTestDatabase NPE

Protect against the situation where no DataSource beans can be found
at all.

Fixes gh-6897

spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/orm/jpa/AutoConfigureTestDatabaseWithNoDatabaseIntegrationTests.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2012-2016 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.boot.test.autoconfigure.orm.jpa;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.context.ApplicationContext;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for {@link AutoConfigureTestDatabase} when there is no database.
+ *
+ * @author Phillip Webb
+ */
+@RunWith(SpringRunner.class)
+@AutoConfigureTestDatabase
+public class AutoConfigureTestDatabaseWithNoDatabaseIntegrationTests {
+
+	@Autowired
+	private ApplicationContext context;
+
+	@Test
+	public void testContextLoades() throws Exception {
+		// gh-6897
+		assertThat(this.context).isNotNull();
+	}
+
+	@SpringBootConfiguration
+	static class Config {
+
+	}
+
+}