add test

hutool-core/src/main/java/cn/hutool/core/text/finder/LengthFinder.java

@@ -19,6 +19,7 @@ public class LengthFinder extends TextFinder {
 	 * @param length 长度
 	 */
 	public LengthFinder(final int length) {
+		Assert.isTrue(length > 0, "Length must be great than 0");
 		this.length = length;
 	}
 

hutool-core/src/test/java/cn/hutool/core/text/SplitUtilTest.java

@@ -0,0 +1,15 @@
+package cn.hutool.core.text;
+
+import cn.hutool.core.text.split.SplitUtil;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SplitUtilTest {
+
+	@Test
+	public void issueI6FKSITest(){
+		// issue:I6FKSI
+		Assert.assertThrows(IllegalArgumentException.class, () -> SplitUtil.splitByLength("test length 0", 0));
+	}
+
+}