Fix directory not existing issue (#237)

* Fix directory not existing issue;
Add UT for agent file downloading;

center/src/main/java/com/microsoft/hydralab/center/service/AgentManageService.java

@@ -136,6 +136,12 @@ public File generateAgentConfigFile(String agentId) {
         AgentUser agentUser = getAgent(agentId);
         if (agentUser != null) {
             try {
+                File tempFolder = new File(CenterConstant.CENTER_TEMP_FILE_DIR);
+                if (!tempFolder.exists()){
+                    if (!tempFolder.mkdirs()) {
+                        throw new RuntimeException("mkdirs fail for: " + tempFolder);
+                    }
+                }
                 File agentConfigFile = File.createTempFile(
                         "application",
                         ".yml",

center/src/test/java/com/microsoft/hydralab/center/service/AgentManageServiceTest.java

@@ -0,0 +1,28 @@
+package com.microsoft.hydralab.center.service;
+
+import com.microsoft.hydralab.common.entity.center.AgentUser;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+import java.io.File;
+
+import static org.mockito.Mockito.doReturn;
+
+public class AgentManageServiceTest {
+
+    @Test
+    void putData() {
+        String agentId = "test_agent_id";
+        AgentManageService agentManageService = Mockito.spy(AgentManageService.class);
+        AgentUser agent = new AgentUser();
+        agent.setName("Agent Name");
+        agent.setId(agentId);
+        agent.setSecret("Agent Secret");
+        doReturn(agent).when(agentManageService).getAgent(agentId);
+
+        File file = agentManageService.generateAgentConfigFile(agentId);
+        Assertions.assertNotNull(file, "Get agent user error");
+        Assertions.assertTrue(file.length() > 0, "Write agent config file error");
+    }
+}