Add tests for GCD and PrimeCheck (#3062)

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

@@ -0,0 +1,41 @@
+package com.thealgorithms.maths;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class PrimeCheckTest {
+    @Test
+    void test1() {
+        Assertions.assertTrue(PrimeCheck.isPrime(2));
+    }
+
+    @Test
+    void test2() {
+        Assertions.assertFalse(PrimeCheck.isPrime(-1));
+    }
+
+    @Test
+    void test3() {
+        Assertions.assertFalse(PrimeCheck.isPrime(4));
+    }
+
+    @Test
+    void test4() {
+        Assertions.assertTrue(PrimeCheck.isPrime(5));
+    }
+
+    @Test
+    void test5() {
+        Assertions.assertFalse(PrimeCheck.isPrime(15));
+    }
+
+    @Test
+    void test6() {
+        Assertions.assertTrue(PrimeCheck.isPrime(11));
+    }
+
+    @Test
+    void test7() {
+        Assertions.assertFalse(PrimeCheck.isPrime(49));
+    }
+}