[TD-6389]<test>: test jdbc use now insert timestamp (#7624)

src/connector/jdbc/src/test/java/com/taosdata/jdbc/cases/UseNowInsertTimestampTest.java

+package com.taosdata.jdbc.cases;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.sql.*;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class UseNowInsertTimestampTest {
+    String url = "jdbc:TAOS://127.0.0.1:6030/?user=root&password=taosdata";
+
+    @Test
+    public void millisec() {
+        try (Connection conn = DriverManager.getConnection(url)) {
+            Statement stmt = conn.createStatement();
+            stmt.execute("drop database if exists test");
+            stmt.execute("create database if not exists test precision 'ms'");
+            stmt.execute("use test");
+            stmt.execute("create table weather(ts timestamp, f1 int)");
+            stmt.execute("insert into weather values(now, 1)");
+
+            ResultSet rs = stmt.executeQuery("select * from weather");
+            rs.next();
+            Timestamp ts = rs.getTimestamp("ts");
+            assertEquals(13, Long.toString(ts.getTime()).length());
+
+            int nanos = ts.getNanos();
+            assertEquals(0, nanos % 1000_000);
+
+            stmt.execute("drop database if exists test");
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+    }
+
+    @Test
+    public void microsec() {
+        try (Connection conn = DriverManager.getConnection(url)) {
+            Statement stmt = conn.createStatement();
+            stmt.execute("drop database if exists test");
+            stmt.execute("create database if not exists test precision 'us'");
+            stmt.execute("use test");
+            stmt.execute("create table weather(ts timestamp, f1 int)");
+            stmt.execute("insert into weather values(now, 1)");
+
+            ResultSet rs = stmt.executeQuery("select * from weather");
+            rs.next();
+            Timestamp ts = rs.getTimestamp("ts");
+            int nanos = ts.getNanos();
+
+            assertEquals(0, nanos % 1000);
+
+            stmt.execute("drop database if exists test");
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+    }
+
+    @Test
+    public void nanosec() {
+        try (Connection conn = DriverManager.getConnection(url)) {
+            Statement stmt = conn.createStatement();
+            stmt.execute("drop database if exists test");
+            stmt.execute("create database if not exists test precision 'ns'");
+            stmt.execute("use test");
+            stmt.execute("create table weather(ts timestamp, f1 int)");
+            stmt.execute("insert into weather values(now, 1)");
+
+            ResultSet rs = stmt.executeQuery("select * from weather");
+            rs.next();
+
+            Timestamp ts = rs.getTimestamp("ts");
+
+            int nanos = ts.getNanos();
+            assertTrue(nanos % 1000 != 0);
+
+            stmt.execute("drop database if exists test");
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+    }
+}