Add twin prime (#3312)

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

@@ -0,0 +1,60 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class TwinPrimeTest {
+
+	@Test
+	void shouldReturn7() {
+		//given
+		int number = 5;
+		int expectedResult = 7;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+	
+	@Test
+	void shouldReturn5() {
+		//given
+		int number = 3;
+		int expectedResult = 5;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+	
+	@Test
+	void shouldReturnNegative1() {
+		//given
+		int number = 4;
+		int expectedResult = -1;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+	
+	@Test
+	void shouldReturn19() {
+		//given
+		int number = 17;
+		int expectedResult = 19;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+}