test: Use kotest

src/main/kotlin/util/TestUtil.kt

@@ -1,5 +1,8 @@
 package moe.nea.firmament.util
 
 object TestUtil {
-	val isInTest = Thread.currentThread().stackTrace.any { it.className.startsWith("org.junit.") }
+	val isInTest =
+		Thread.currentThread().stackTrace.any {
+			it.className.startsWith("org.junit.") || it.className.startsWith("io.kotest.")
+		}
 }