last n characters from string unit tests

core-java-modules/core-java-string-operations-8/src/test/java/com/baeldung/lastncharacters/LastNCharactersUnitTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.lastncharacters;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+import org.apache.commons.lang3.ArrayUtils;
+import org.apache.commons.lang3.StringUtils;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class LastNCharactersUnitTest {
+
+    private String s;
+    private int n;
+
+    @Test
+    void givenString_whenUsingIntStreamAsStreamSource_thenObtainLastNCharacters() {
+        String result = s.chars()
+            .mapToObj(c -> (char) c)
+            .skip(s.length() - n)
+            .map(String::valueOf)
+            .collect(Collectors.joining());
+        assertThat(result).isEqualTo("2024");
+    }
+
+    @Test
+    void givenString_whenUsingOneArgSubstringMethod_thenObtainLastNCharacters() {
+        int beginIndex = s.length() - n;
+        assertThat(s.substring(beginIndex)).isEqualTo("2024");
+    }
+
+    @Test
+    void givenString_whenUsingStreamOfCharactersAsSource_thenObtainLastNCharacters() {
+        String result = Arrays.stream(ArrayUtils.toObject(s.toCharArray()))
+            .skip(s.length() - n)
+            .map(String::valueOf)
+            .collect(Collectors.joining());
+        assertThat(result).isEqualTo("2024");
+    }
+
+    @Test
+    void givenString_whenUsingStringUtilsRight_thenObtainLastNCharacters() {
+        assertThat(StringUtils.right(s, n)).isEqualTo("2024");
+    }
+
+    @Test
+    void givenString_whenUsingTwoArgSubstringMethod_thenObtainLastNCharacters() {
+        int beginIndex = s.length() - n;
+        String result = s.substring(beginIndex, s.length());
+        assertThat(result).isEqualTo("2024");
+    }
+
+    @BeforeEach
+    void init() {
+        s = "10-03-2024";
+        n = 4;
+    }
+}