[unit test] Add unit test cases for AlertTemplateUtil (#639)

alerter/src/test/java/com/usthe/alert/util/AlertTemplateUtilTest.java

@@ -1,21 +1,65 @@
 package com.usthe.alert.util;
 
-import com.usthe.alert.service.AlertService;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import java.util.HashMap;
+import java.util.Map;
+
 import static org.junit.jupiter.api.Assertions.*;
 
 /**
  * Test case for {@link AlertTemplateUtil}
  */
 class AlertTemplateUtilTest {
 
+    class TemplateValue {
+
+    }
+
     @BeforeEach
     void setUp() {
     }
 
     @Test
     void render() {
+        // test null template case
+        Map<String, Object> param = new HashMap<>();
+        String template = null;
+        assertNull(AlertTemplateUtil.render(null, param));
+        // test null map case
+        template = "${key} for testing";
+        assertEquals(AlertTemplateUtil.render(template, null), template);
+        // test null template and null map case
+        assertNull(AlertTemplateUtil.render(null, null));
+        // test illegal template case
+        template = "";
+        param.put("key", "Just");
+        assertEquals(AlertTemplateUtil.render(template, param), template);
+        template = "key for testing!";
+        assertEquals(AlertTemplateUtil.render(template, param), template);
+        // test empty map case
+        param.clear();
+        template = "${key} for testing";
+        assertEquals(AlertTemplateUtil.render(template, param), "NullValue for testing");
+        // test illegal template and empty map case
+        param.clear();
+        template = "key for testing";
+        assertEquals(AlertTemplateUtil.render(template, param), template);
+        // test one param
+        param.put("key", "Just");
+        template = "${key} for testing";
+        assertEquals(AlertTemplateUtil.render(template, param), "Just for testing");
+        // test two param
+        param.put("key1", "Just");
+        param.put("key2", "testing");
+        template = "${key1} for ${key2}";
+        assertEquals(AlertTemplateUtil.render(template, param), "Just for testing");
+        // test all param
+        param.put("key1", "Just");
+        param.put("key2", "for");
+        param.put("key3", "testing");
+        template = "${key1} ${key2} ${key3}";
+        assertEquals(AlertTemplateUtil.render(template, param), "Just for testing");
     }
 }