[Util] Fix cached priority ordering after insertion

usvm-util/src/main/kotlin/org/usvm/algorithms/DeterministicPriorityCollection.kt

@@ -44,7 +44,7 @@ class DeterministicPriorityCollection<T, Priority>(private val comparator: Compa
         assert({ !priorityQueue.any { (e, _) -> e == element } }) { "Element already exists in priority queue" }
 
         val currentTop = topElement
-        if (currentTop != null && comparator.compare(currentTop.second, priority) < 0) {
+        if (currentTop != null && comparator.compare(currentTop.second, priority) > 0) {
             topElement = element to priority
             priorityQueue.add(currentTop)
             return

usvm-util/src/test/kotlin/org/usvm/algorithms/DeterministicPriorityCollectionTest.kt

@@ -0,0 +1,62 @@
+package org.usvm.algorithms
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+internal class DeterministicPriorityCollectionTest {
+    @Test
+    fun `adding a worse priority keeps the cached minimum`() {
+        val collection = DeterministicPriorityCollection<String, Int>(naturalOrder())
+        collection.add(element = "first", priority = 1)
+        assertEquals("first", collection.peek())
+
+        collection.add(element = "second", priority = 2)
+
+        assertEquals("first", collection.peek())
+        collection.remove("first")
+        assertEquals("second", collection.peek())
+        assertEquals(1, collection.count)
+    }
+
+    @Test
+    fun `adding a better priority replaces the cached minimum`() {
+        val collection = DeterministicPriorityCollection<String, Int>(naturalOrder())
+        collection.add(element = "second", priority = 2)
+        assertEquals("second", collection.peek())
+
+        collection.add(element = "first", priority = 1)
+
+        assertEquals("first", collection.peek())
+        collection.remove("first")
+        assertEquals("second", collection.peek())
+        assertEquals(1, collection.count)
+    }
+
+    @Test
+    fun `adding a worse priority keeps the cached maximum with reverse order`() {
+        val collection = DeterministicPriorityCollection<String, Int>(reverseOrder())
+        collection.add(element = "first", priority = 2)
+        assertEquals("first", collection.peek())
+
+        collection.add(element = "second", priority = 1)
+
+        assertEquals("first", collection.peek())
+        collection.remove("first")
+        assertEquals("second", collection.peek())
+        assertEquals(1, collection.count)
+    }
+
+    @Test
+    fun `adding a better priority replaces the cached maximum with reverse order`() {
+        val collection = DeterministicPriorityCollection<String, Int>(reverseOrder())
+        collection.add(element = "second", priority = 1)
+        assertEquals("second", collection.peek())
+
+        collection.add(element = "first", priority = 2)
+
+        assertEquals("first", collection.peek())
+        collection.remove("first")
+        assertEquals("second", collection.peek())
+        assertEquals(1, collection.count)
+    }
+}