fixes in built-in schedulers

src/commonTest/kotlin/BuildersTest.kt

@@ -0,0 +1,38 @@
+package dev.inmo.krontab.utils
+
+import dev.inmo.krontab.*
+import korlibs.time.*
+import kotlinx.coroutines.test.runTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.time.Duration.Companion.milliseconds
+import kotlin.time.Duration.Companion.minutes
+import kotlin.time.Duration.Companion.seconds
+
+class BuildersTest {
+    @Test
+    fun presetsWorksCorrectly() {
+        val data = mapOf(
+            EverySecondScheduler to { it: DateTime -> if (it.milliseconds > 0 ) it + 1.seconds - it.milliseconds.milliseconds else it },
+            EveryMinuteScheduler to { it: DateTime -> if (it.seconds > 0 || it.milliseconds > 0 ) it + 1.minutes - it.seconds.seconds - it.milliseconds.milliseconds else it },
+            EveryHourScheduler to { it: DateTime -> if (it.minutes > 0 || it.seconds > 0 || it.milliseconds > 0 ) it + 1.hours - it.minutes.minutes - it.seconds.seconds - it.milliseconds.milliseconds else it },
+            EveryDayOfMonthScheduler to { it: DateTime -> if (it.hours > 0 || it.minutes > 0 || it.seconds > 0 || it.milliseconds > 0 ) it + 1.days - it.hours.hours - it.minutes.minutes - it.seconds.seconds - it.milliseconds.milliseconds else it },
+            EveryMonthScheduler to { it: DateTime -> if (it.dayOfMonth > 1 || it.hours > 0 || it.minutes > 0 || it.seconds > 0 || it.milliseconds > 0 ) (it + 1.months).copy(dayOfMonth = 1, hour = 0, minute = 0, second = 0, milliseconds = 0) else it },
+        )
+        val samples = 10000
+
+        runTest {
+            var now = DateTime.now()
+            for (i in 0 until samples) {
+                data.forEach { (scheduler, expectCalculator) ->
+                    val expectValue = expectCalculator(now)
+                    val newNow = scheduler.nextOrRelative(now)
+
+                    assertEquals(expectValue, newNow, "For time ${now.toStringDefault()} calculated wrong value: ${newNow.toStringDefault()} is not equal to ${expectValue.toStringDefault()}")
+
+                    now = newNow
+                }
+            }
+        }
+    }
+}