baeldung-articles : BAEL-7442 (#15887)

* baeldung-articles : BAEL-7442

Check if String is Base64 Encoded (commit)

* Update CheckIfStringIsBased64UnitTest.java

core-java-modules/core-java-string-operations-8/src/test/java/com/baeldung/checkifstringisbased64/CheckIfStringIsBased64UnitTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.checkifstringisbased64;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Base64;
+import java.util.regex.Pattern;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class CheckIfStringIsBased64UnitTest {
+
+    @Test
+    public void givenBase64EncodedString_whenDecoding_thenNoException() {
+        try {
+            Base64.getDecoder().decode("SGVsbG8gd29ybGQ=");
+            assertTrue(true);
+        } catch (IllegalArgumentException e) {
+            fail("Unexpected exception: " + e.getMessage());
+        }
+    }
+
+    @Test
+    public void givenNonBase64String_whenDecoding_thenCatchException() {
+        try {
+            Base64.getDecoder().decode("Hello world!");
+            fail("Expected IllegalArgumentException was not thrown");
+        } catch (IllegalArgumentException e) {
+            assertTrue(true);
+        }
+    }
+
+    @Test
+    public void givenString_whenOperatingRegex_thenCheckIfItIsBase64Encoded() {
+        Pattern BASE64_PATTERN = Pattern.compile(
+                "^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$"
+        );
+
+        assertTrue(BASE64_PATTERN.matcher("SGVsbG8gd29ybGQ=").matches());
+    }
+}