Add test for concat to verify distribution of UnconditionalModification after NumberSpanParserOperation.

Author: DmitryNekrasov

core/common/test/format/ParserStructureConcatenationTest.kt

@@ -8,13 +8,46 @@ package kotlinx.datetime.test.format
 import kotlinx.datetime.internal.format.parser.ConstantNumberConsumer
 import kotlinx.datetime.internal.format.parser.NumberSpanParserOperation
 import kotlinx.datetime.internal.format.parser.ParserStructure
+import kotlinx.datetime.internal.format.parser.UnconditionalModification
 import kotlinx.datetime.internal.format.parser.concat
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertTrue
 
 class ParserStructureConcatenationTest {
 
+    @Test
+    fun concatDistributesUnconditionalModificationAfterNumberSpanParserOperation() {
+        val parser = ParserStructure<Int>(
+            operations = listOf(
+                UnconditionalModification { }
+            ),
+            followedBy = listOf(
+                ParserStructure(
+                    operations = listOf(
+                        NumberSpanParserOperation(listOf(ConstantNumberConsumer("34")))
+                    ),
+                    followedBy = listOf()
+                )
+            )
+        )
+
+        val actual = listOf(parser).concat()
+
+        with(actual) {
+            assertTrue(operations.isEmpty())
+            with(followedBy) {
+                assertEquals(1, size)
+                with(followedBy[0]) {
+                    assertEquals(2, operations.size)
+                    assertTrue(operations[0] is NumberSpanParserOperation)
+                    assertTrue(operations[1] is UnconditionalModification)
+                    assertTrue(followedBy.isEmpty())
+                }
+            }
+        }
+    }
+
     @Test
     fun concatFlattensOperations() {
         val parser = ParserStructure<Int>(