diff --git a/main/tests/server/src/com/google/refine/tests/expr/functions/date/DatePartTests.java b/main/tests/server/src/com/google/refine/tests/expr/functions/date/DatePartTests.java
new file mode 100644
index 000000000..f9830e037
--- /dev/null
+++ b/main/tests/server/src/com/google/refine/tests/expr/functions/date/DatePartTests.java
@@ -0,0 +1,244 @@
+package com.google.refine.tests.expr.functions.date;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.time.OffsetDateTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeFormatterBuilder;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.Properties;
+import java.util.TimeZone;
+
+import org.slf4j.LoggerFactory;
+import org.testng.Assert;
+import org.testng.annotations.AfterMethod;
+import org.testng.annotations.BeforeMethod;
+import org.testng.annotations.BeforeTest;
+import org.testng.annotations.Test;
+
+import com.google.refine.expr.EvalError;
+import com.google.refine.grel.ControlFunctionRegistry;
+import com.google.refine.grel.Function;
+import com.google.refine.tests.RefineTest;
+
+
+public class DatePartTests extends RefineTest {
+
+    static Properties bindings;
+    
+    @Override
+    @BeforeTest
+    public void init() {
+        logger = LoggerFactory.getLogger(this.getClass());
+    }
+    
+    @BeforeMethod
+    public void SetUp() {
+        bindings = new Properties();
+    }
+
+    @AfterMethod
+    public void TearDown() {
+        bindings = null;
+    }
+    
+    /**
+     * Lookup a control function by name and invoke it with a variable number of args
+     */
+    private static Object invoke(String name,Object... args) {
+        // registry uses static initializer, so no need to set it up
+        Function function = ControlFunctionRegistry.getFunction(name);
+        if (function == null) {
+            throw new IllegalArgumentException("Unknown function "+name);
+        }
+        if (args == null) {
+            return function.call(bindings,new Object[0]);
+        } else {
+            return function.call(bindings,args);
+        }
+    }
+    
+    @Test
+    public void testDateDatePart() throws ParseException {        
+        Assert.assertTrue(invoke("datePart") instanceof EvalError);
+        
+        // 2018-4-30 23:55:44, cannot use new Date(2018 - 1900, 4 - 1, 30, 23, 55, 44). use below way to get a UTC date:
+        SimpleDateFormat isoFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
+        isoFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
+        Date source = isoFormat.parse("2018-04-30T23:55:44");
+        
+        // hours
+        Assert.assertEquals(invoke("datePart", source, "hours"), 23);
+        Assert.assertEquals(invoke("datePart", source, "hour"), 23);
+        Assert.assertEquals(invoke("datePart", source, "h"), 23);
+        
+        // minutes
+        Assert.assertEquals(invoke("datePart", source, "minutes"), 55);
+        Assert.assertEquals(invoke("datePart", source, "minute"), 55);
+        Assert.assertEquals(invoke("datePart", source, "min"), 55);
+        
+        // seconds
+        Assert.assertEquals(invoke("datePart", source, "seconds"), 44);
+        Assert.assertEquals(invoke("datePart", source, "sec"), 44);
+        Assert.assertEquals(invoke("datePart", source, "s"), 44);
+        
+        // milliseconds
+        Assert.assertEquals(invoke("datePart", source, "milliseconds"), 0);
+        Assert.assertEquals(invoke("datePart", source, "ms"), 0);
+        Assert.assertEquals(invoke("datePart", source, "S"), 0);
+        
+        // years
+        Assert.assertEquals(invoke("datePart", source, "years"), 2018);
+        Assert.assertEquals(invoke("datePart", source, "year"), 2018);
+        
+        // months
+        Assert.assertEquals(invoke("datePart", source, "months"), 4);
+        Assert.assertEquals(invoke("datePart", source, "month"), 4);
+        
+        // weeks
+        Assert.assertEquals(invoke("datePart", source, "weeks"), 5);
+        Assert.assertEquals(invoke("datePart", source, "week"), 5);
+        Assert.assertEquals(invoke("datePart", source, "w"), 5);
+        
+        // days, day, d
+        Assert.assertEquals(invoke("datePart", source, "days"), 30);
+        Assert.assertEquals(invoke("datePart", source, "day"), 30);
+        Assert.assertEquals(invoke("datePart", source, "d"), 30);
+        
+        // weekday
+        Assert.assertEquals(invoke("datePart", source, "weekday"), "Monday");
+        
+        // time
+        Assert.assertEquals(invoke("datePart", source, "time"), 1525132544000l);
+    }
+    
+    @Test
+    public void testCalendarDatePart() throws ParseException {        
+     // 2018-4-30 23:55:44
+        SimpleDateFormat isoFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
+        isoFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
+        Date dt = isoFormat.parse("2018-04-30T23:55:44");
+        Calendar source = dateToCalendar(dt);
+        source.set(Calendar.MILLISECOND, 789);
+        
+        // hours
+        Assert.assertEquals(invoke("datePart", source, "hours"), 23);
+        Assert.assertEquals(invoke("datePart", source, "hour"), 23);
+        Assert.assertEquals(invoke("datePart", source, "h"), 23);
+        
+        // minutes
+        Assert.assertEquals(invoke("datePart", source, "minutes"), 55);
+        Assert.assertEquals(invoke("datePart", source, "minute"), 55);
+        Assert.assertEquals(invoke("datePart", source, "min"), 55);
+        
+        // seconds
+        Assert.assertEquals(invoke("datePart", source, "seconds"), 44);
+        Assert.assertEquals(invoke("datePart", source, "sec"), 44);
+        Assert.assertEquals(invoke("datePart", source, "s"), 44);
+        
+        // milliseconds
+        Assert.assertEquals(invoke("datePart", source, "milliseconds"), 789);
+        Assert.assertEquals(invoke("datePart", source, "ms"), 789);
+        Assert.assertEquals(invoke("datePart", source, "S"), 789);
+        
+        // years
+        Assert.assertEquals(invoke("datePart", source, "years"), 2018);
+        Assert.assertEquals(invoke("datePart", source, "year"), 2018);
+        
+        // months
+        Assert.assertEquals(invoke("datePart", source, "months"), 4);
+        Assert.assertEquals(invoke("datePart", source, "month"), 4);
+        
+        // weeks
+        Assert.assertEquals(invoke("datePart", source, "weeks"), 5);
+        Assert.assertEquals(invoke("datePart", source, "week"), 5);
+        Assert.assertEquals(invoke("datePart", source, "w"), 5);
+        
+        // days, day, d
+        Assert.assertEquals(invoke("datePart", source, "days"), 30);
+        Assert.assertEquals(invoke("datePart", source, "day"), 30);
+        Assert.assertEquals(invoke("datePart", source, "d"), 30);
+        
+        // weekday
+        Assert.assertEquals(invoke("datePart", source, "weekday"), "Monday");
+        
+        // time
+        Assert.assertEquals(invoke("datePart", source, "time"), 1525132544000l + 789);
+    }
+    
+    private DateTimeFormatter formatter = new DateTimeFormatterBuilder()
+            // here is the same as your code
+            .append(DateTimeFormatter.BASIC_ISO_DATE).appendLiteral('-')
+            // time (hour/minute/seconds)
+            .appendPattern("HH:mm:ss")
+            // optional nanos, with 9, 6 or 3 digits
+            .appendPattern("[.SSSSSSSSS][.SSSSSS][.SSS]")
+            // offset
+            .appendOffset("+HH:mm", "Z")
+            // create formatter
+            .toFormatter();
+    
+    @Test
+    public void testOffsetDateTimeDatePart() {        
+        // 2018-4-30 23:55:44
+        OffsetDateTime source = OffsetDateTime.parse("20180430-23:55:44.000789000Z",
+                formatter);
+        
+        // hours
+        Assert.assertEquals(invoke("datePart", source, "hours"), 23);
+        Assert.assertEquals(invoke("datePart", source, "hour"), 23);
+        Assert.assertEquals(invoke("datePart", source, "h"), 23);
+        
+        // minutes
+        Assert.assertEquals(invoke("datePart", source, "minutes"), 55);
+        Assert.assertEquals(invoke("datePart", source, "minute"), 55);
+        Assert.assertEquals(invoke("datePart", source, "min"), 55);
+        
+        // seconds
+        Assert.assertEquals(invoke("datePart", source, "seconds"), 44);
+        Assert.assertEquals(invoke("datePart", source, "sec"), 44);
+        Assert.assertEquals(invoke("datePart", source, "s"), 44);
+        
+        // milliseconds
+        Assert.assertEquals(invoke("datePart", source, "milliseconds"), 789);
+        Assert.assertEquals(invoke("datePart", source, "ms"), 789);
+        Assert.assertEquals(invoke("datePart", source, "S"), 789);
+        
+        // nanos
+        Assert.assertEquals(invoke("datePart", source, "nanos"), 789000);
+        Assert.assertEquals(invoke("datePart", source, "nano"), 789000);
+        Assert.assertEquals(invoke("datePart", source, "n"), 789000);
+        
+        // years
+        Assert.assertEquals(invoke("datePart", source, "years"), 2018);
+        Assert.assertEquals(invoke("datePart", source, "year"), 2018);
+        
+        // months
+        Assert.assertEquals(invoke("datePart", source, "months"), 4);
+        Assert.assertEquals(invoke("datePart", source, "month"), 4);
+        
+        // weeks
+        Assert.assertEquals(invoke("datePart", source, "weeks"), 5);
+        Assert.assertEquals(invoke("datePart", source, "week"), 5);
+        Assert.assertEquals(invoke("datePart", source, "w"), 5);
+        
+        // days, day, d
+        Assert.assertEquals(invoke("datePart", source, "days"), 30);
+        Assert.assertEquals(invoke("datePart", source, "day"), 30);
+        Assert.assertEquals(invoke("datePart", source, "d"), 30);
+        
+        // weekday
+        Assert.assertEquals(invoke("datePart", source, "weekday"), "MONDAY");
+        
+        // time
+        Assert.assertEquals(invoke("datePart", source, "time"), 1525132544000l);
+    }
+    
+    // Convert Date to Calendar
+    private Calendar dateToCalendar(Date date) {
+        Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
+        calendar.setTime(date);
+        return calendar;
+    }
+}
\ No newline at end of file