Add test case for OctalToDecimal (#3678)

src/test/java/com/thealgorithms/conversions/OctalToDecimalTest.java

@@ -0,0 +1,14 @@
+package com.thealgorithms.conversions;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class OctalToDecimalTest {
+
+    @Test
+    public void testOctalToDecimal() {
+        assertEquals(1465, OctalToDecimal.convertOctalToDecimal("2671"));
+        assertEquals(189, OctalToDecimal.convertOctalToDecimal("275"));
+    }
+}