修复FastDatePrinter处理YY错误问题

hutool-core/src/test/java/cn/hutool/core/date/FastDateFormatTest.java

@@ -0,0 +1,58 @@
+package cn.hutool.core.date;
+
+import cn.hutool.core.date.format.FastDateFormat;
+import org.junit.Test;
+
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.TimeZone;
+
+import static org.junit.Assert.assertEquals;
+
+public class FastDateFormatTest {
+	private static final TimeZone timezone = TimeZone.getTimeZone("Etc/Utc");
+
+	private static FastDateFormat getHutoolInstance(String pattern) {
+		return FastDateFormat.getInstance(pattern, timezone);
+	}
+
+	@Test
+	public void yearTest() {
+		Date date = DateUtil.date(0L);
+
+		assertEquals(
+			"1970-01-01 00:00:00",
+			getHutoolInstance("yyyy-MM-dd HH:mm:ss").format(date)
+		);
+
+		assertEquals(
+			"1970-01-01 00:00:00",
+			getHutoolInstance("YYYY-MM-dd HH:mm:ss").format(date)
+		);
+
+		assertEquals(
+			"1970",
+			getHutoolInstance("YYYY").format(date)
+		);
+
+		assertEquals(
+			"70",
+			getHutoolInstance("yy").format(date)
+		);
+	}
+
+	@Test
+	public void weekYearTest() {
+		Date date = DateUtil.date(0L);
+
+		assertEquals(
+			"70",
+			new SimpleDateFormat("YY").format(date)
+		);
+
+		assertEquals(
+			"70",
+			getHutoolInstance("YY").format(date)
+		);
+	}
+}