Add test case to Binomial Coefficient Algorithm (#3179)

Co-authored-by: Yang Libin <contact@yanglibin.info>

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

@@ -0,0 +1,18 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class BinomialCoefficientTest {
+
+    @Test
+    void testBinomialCoefficient() {
+
+        assertEquals(190, BinomialCoefficient.binomialCoefficient(20, 2));
+        assertEquals(792, BinomialCoefficient.binomialCoefficient(12, 5));
+        assertEquals(84, BinomialCoefficient.binomialCoefficient(9, 3));
+        assertEquals(1, BinomialCoefficient.binomialCoefficient(17, 17));
+
+    }
+}