Added tests for FactorialRecursion

Author: Maria Paszkiewicz SCC

src/main/java/com/thealgorithms/maths/FactorialRecursion.java

@@ -1,16 +1,8 @@
 package com.thealgorithms.maths;
 
-public class FactorialRecursion {
-
-    /* Driver Code */
-    public static void main(String[] args) {
-        assert factorial(0) == 1;
-        assert factorial(1) == 1;
-        assert factorial(2) == 2;
-        assert factorial(3) == 6;
-        assert factorial(5) == 120;
+public final class FactorialRecursion {
+    private FactorialRecursion() {
     }
-
     /**
      * Recursive FactorialRecursion Method
      *

src/test/java/com/thealgorithms/maths/FactorialRecursionTest.java

@@ -0,0 +1,28 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class FactorialRecursionTest {
+    @ParameterizedTest
+    @MethodSource("inputStream")
+    void testFactorialRecursion(long expected, int number) {
+        assertEquals(expected, FactorialRecursion.factorial(number));
+    }
+
+    private static Stream<Arguments> inputStream() {
+        return Stream.of(Arguments.of(1, 0), Arguments.of(1, 1), Arguments.of(2, 2), Arguments.of(6, 3), Arguments.of(120, 5));
+    }
+
+    @Test
+    void testNegativeNumber() {
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> FactorialRecursion.factorial(-1));
+    }
+}