StatefulFetchService to save last 24h of data

src/test/scala/fetch/FileNameServiceSpec.scala

@@ -1,10 +1,16 @@
+import cats.Applicative
+import cats.effect.unsafe.implicits.global
 import fetch.FileNameService
 import org.scalatest.funsuite.AnyFunSuite
+import cats.effect.{Clock, IO}
 
+import java.util.concurrent.TimeUnit
 import java.time.LocalDateTime
+import scala.concurrent.duration.FiniteDuration
+import scala.concurrent.duration._
+
 
 class FileNameServiceSpec extends AnyFunSuite {
-
   test("FileNameService.generate returns correct file names") {
     val startTime = LocalDateTime.of(2023, 5, 17, 0, 0)
     val endTime = LocalDateTime.of(2023, 5, 17, 4, 0)
@@ -25,11 +31,40 @@ class FileNameServiceSpec extends AnyFunSuite {
     val date = LocalDateTime.of(2023, 5, 17, 0, 0).toLocalDate
 
     val expectedFileNames = (0 to 23).toList
-      .map(hour => if(hour < 10) "0"+hour else ""+hour)
+      .map(hour => if (hour < 10) "0" + hour else "" + hour)
       .map(str => s"20230517_${str}30.csv")
 
     val actualFileNames = new FileNameService().generateFromDate(date)
 
     assert(actualFileNames == expectedFileNames)
   }
+
+  val fixedClock: Clock[IO] = new Clock[IO] {
+    val timeInMillis = 1618862447000L
+
+    override def realTime: IO[FiniteDuration] =
+      IO.pure(Duration.fromNanos(TimeUnit.MILLISECONDS.toNanos(timeInMillis)))
+
+    override def applicative: Applicative[IO] =
+      Applicative.apply
+
+    override def monotonic: IO[FiniteDuration] =
+      IO.pure(Duration.fromNanos(TimeUnit.MILLISECONDS.toNanos(timeInMillis)))
+
+    override def timed[A](fa: IO[A]): IO[(FiniteDuration, A)] =
+      fa.map(a => (Duration.Zero, a))
+  }
+
+  test("FileNameService.generateLast24Hours returns correct file names for a fixed time") {
+    val fileNameService = new FileNameService()
+    val filenames = fileNameService.generateLast24Hours(fixedClock).unsafeRunSync()
+
+    assert(filenames.size == 24)
+
+    val expectedFileNames = (0 to 23).toList
+      .map(hour => if (hour < 10) "0" + hour else "" + hour)
+      .map(str => s"20210419_${str}30.csv")
+
+    assert(filenames.sorted == expectedFileNames.sorted)
+  }
 }