add DeviceCredentials#toString

src/main/java/com/telekom/m2m/cot/restsdk/devicecontrol/DeviceCredentials.java

@@ -40,4 +40,12 @@ public String getTenantId() {
     public String getUsername() {
         return username;
     }
+
+    @Override
+    public String toString() {
+        return "DeviceCredentials{" + "id='" + id + '\'' +
+                ", tenantId='" + tenantId + '\'' +
+                ", username='" + username + '\'' +
+                '}';
+    }
 }

src/test/java/com/telekom/m2m/cot/restsdk/devicecontrol/DeviceCredentialsTest.java

@@ -0,0 +1,29 @@
+package com.telekom.m2m.cot.restsdk.devicecontrol;
+
+import org.testng.annotations.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+public class DeviceCredentialsTest {
+
+    @Test
+    public void testToString() {
+
+        final DeviceCredentials deviceCredentials = new DeviceCredentials();
+
+        deviceCredentials.setId("id_" + System.currentTimeMillis());
+        deviceCredentials.setUsername("username_" + System.currentTimeMillis());
+        deviceCredentials.setPassword("password_" + System.currentTimeMillis());
+        deviceCredentials.setTenantId("tenantId_" + System.currentTimeMillis());
+
+        final String stringRepresentation = deviceCredentials.toString();
+        assertNotNull(stringRepresentation);
+        assertFalse(stringRepresentation.contains(deviceCredentials.getPassword()));
+        assertTrue(stringRepresentation.contains(deviceCredentials.getId()));
+        assertTrue(stringRepresentation.contains(deviceCredentials.getUsername()));
+        assertTrue(stringRepresentation.contains(deviceCredentials.getTenantId()));
+    }
+
+}