add half-life test

Author: danthe1st

src/test/java/net/discordjug/javabot/systems/help/HelpExperienceSubtractionTest.java

@@ -1,6 +1,8 @@
 package net.discordjug.javabot.systems.help;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.IOException;
 import java.sql.SQLException;
@@ -89,6 +91,21 @@ void testFraction() {
 		assertEquals(81, repo.getByUserId(1).get().getExperience());
 	}
 
+	@Test
+	void testXPHalfLife() {
+		int startXP = 1_000;
+		int half = startXP/2;
+		repo.insert(new HelpAccount(1, startXP));
+		for (int i = 0; i < 55; i++) {
+			repo.removeExperienceFromAllAccounts(1.25, 0, 1_000);
+			double actualXP = repo.getByUserId(1).get().getExperience();
+			assertTrue(actualXP > half, "In iteration "+i+", XP have decayed by more than 50%, user has "+actualXP+"XP after iteration");
+		}
+		repo.removeExperienceFromAllAccounts(1.25, 0, 1_000);
+		double actualXP = repo.getByUserId(1).get().getExperience();
+		assertFalse(actualXP > half, "After all iterations, XP have not decayed by more than 50%, user has "+actualXP+"XP at the end");
+	}
+	
 	@Test
 	void testMultipleUsers() {
 		repo.insert(new HelpAccount(79, 79));//below min