diff --git a/src/org/april/agirstatool/core/AgirStatoolUtils.java b/src/org/april/agirstatool/core/AgirStatoolUtils.java
index caa04c6..8dde07d 100644
--- a/src/org/april/agirstatool/core/AgirStatoolUtils.java
+++ b/src/org/april/agirstatool/core/AgirStatoolUtils.java
@@ -577,7 +577,7 @@ public class AgirStatoolUtils
 		}
 		else
 		{
-			result = source.format(DateTimeFormatter.ofPattern("yyyyww", Locale.FRANCE));
+			result = source.format(DateTimeFormatter.ofPattern("YYYYww", Locale.FRANCE));
 		}
 
 		//
diff --git a/test/org/april/agirstatool/core/JugaTest.java b/test/org/april/agirstatool/core/JugaTest.java
index 5b78269..f40ec25 100644
--- a/test/org/april/agirstatool/core/JugaTest.java
+++ b/test/org/april/agirstatool/core/JugaTest.java
@@ -18,10 +18,16 @@
  */
 package org.april.agirstatool.core;
 
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeFormatterBuilder;
+import java.time.format.SignStyle;
+import java.time.temporal.IsoFields;
+import java.util.Locale;
+
 import org.apache.log4j.BasicConfigurator;
 import org.apache.log4j.Level;
 import org.apache.log4j.Logger;
-import org.april.agirstatool.core.AgirStatoolException;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Test;
@@ -45,6 +51,33 @@ public class JugaTest
 		logger.debug("===== test done.");
 	}
 
+	@Test
+	public void testWeek() throws Exception
+	{
+		//
+		logger.debug("===== test starting...");
+
+		System.out.println("==> " + LocalDate.now().getDayOfWeek());
+		System.out.println("==> " + LocalDate.now().getDayOfWeek().getValue());
+		System.out.println("==> " + AgirStatoolUtils.normaliseWeekDate(LocalDate.now()));
+		System.out.println("==> " + AgirStatoolUtils.toYearWeek(LocalDate.of(2019, 12, 30)));
+
+		System.out.println(LocalDate.of(2019, 12, 30).format(DateTimeFormatter.ofPattern("yyyyww", Locale.FRENCH)));
+		System.out.println(LocalDate.of(2019, 12, 30).format(DateTimeFormatter.ofPattern("YYYYww", Locale.FRENCH)));
+		System.out.println(LocalDate.of(2019, 12, 30).format(DateTimeFormatter.ISO_WEEK_DATE));
+
+		DateTimeFormatter weekDateFormatter = new DateTimeFormatterBuilder()
+				.parseCaseInsensitive()
+				.appendValue(IsoFields.WEEK_BASED_YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
+				.appendValue(IsoFields.WEEK_OF_WEEK_BASED_YEAR, 2)
+				.toFormatter(Locale.FRANCE);
+
+		System.out.println(LocalDate.of(2019, 12, 30).format(weekDateFormatter));
+
+		//
+		logger.debug("===== test done.");
+	}
+
 	/**
 	 * After class.
 	 *