add tests for reading server error messages

Author: dehora

intercom-java/src/main/java/io/intercom/api/IntercomException.java

@@ -21,8 +21,12 @@ public IntercomException(ErrorCollection errorCollection) {
     }
 
     public static String getMessage(ErrorCollection errorCollection) {
-        String message = "";
-        if(errorCollection!=null && errorCollection.getErrors() != null && errorCollection.getErrors().size() > 0 && errorCollection.getErrors().get(0) != null){
+        String message = "Could not read error message from server";
+        if(errorCollection!=null
+            && errorCollection.getErrors() != null
+            && errorCollection.getErrors().size() > 0
+            && errorCollection.getErrors().get(0) != null
+            && errorCollection.getErrors().get(0).getMessage() != null){
             message = errorCollection.getErrors().get(0).getMessage();
         }
         return message;

intercom-java/src/test/java/io/intercom/api/IntercomExceptionTest.java

@@ -0,0 +1,32 @@
+package io.intercom.api;
+
+import com.google.common.collect.Lists;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class IntercomExceptionTest {
+
+    @Test
+    public void testNullCollection() {
+        assertEquals("Could not read error message from server", IntercomException.getMessage(null));
+    }
+
+    @Test
+    public void testBlankCollection() {
+        ErrorCollection ec = new ErrorCollection();
+        assertEquals("Could not read error message from server", IntercomException.getMessage(ec));
+    }
+
+    @Test
+    public void testEmptyCollection() {
+        try {
+            new ErrorCollection(Lists.<Error>newArrayList());
+            fail();
+        } catch (IllegalArgumentException e) {
+        }
+        final ErrorCollection ec = new ErrorCollection(Lists.newArrayList(new Error()));
+        assertEquals("Could not read error message from server", IntercomException.getMessage(ec));
+    }
+
+}