Added @before method to clean context before tests

Author: sapessi

aws-serverless-java-container-spring/src/test/java/com/amazonaws/serverless/proxy/spring/SpringAwsProxyTest.java

@@ -2,6 +2,7 @@
 
 import com.amazonaws.serverless.proxy.internal.model.AwsProxyRequest;
 import com.amazonaws.serverless.proxy.internal.model.AwsProxyResponse;
+import com.amazonaws.serverless.proxy.internal.servlet.AwsProxyServletContext;
 import com.amazonaws.serverless.proxy.internal.testutils.AwsProxyRequestBuilder;
 import com.amazonaws.serverless.proxy.internal.testutils.MockLambdaContext;
 import com.amazonaws.serverless.proxy.spring.echoapp.EchoSpringAppConfig;
@@ -10,6 +11,7 @@
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import org.apache.commons.codec.binary.Base64;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -44,6 +46,11 @@ public class SpringAwsProxyTest {
     @Autowired
     private SpringLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler;
 
+    @Before
+    public void clearServletContextCache() {
+        AwsProxyServletContext.clearServletContextCache();
+    }
+
     @Test
     public void headers_getHeaders_echo() {
         AwsProxyRequest request = new AwsProxyRequestBuilder("/echo/headers", "GET")