Add Run-Length Encoding (fixes #3911) (#3916)

src/test/java/com/thealgorithms/strings/StringCompressionTest.java

@@ -0,0 +1,13 @@
+package com.thealgorithms.strings;
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+public class StringCompressionTest {
+    @ParameterizedTest
+    @CsvSource({"a,a","aabbb,a2b3","abbbc,ab3c","aabccd,a2bc2d"})
+    void stringCompressionTest(String input,String expectedOutput){
+        String output=StringCompression.compress(input);
+        assertEquals(expectedOutput, output);
+    }
+}