add test

Author: CarloMariaProietti

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/testSets/person/DataFrameTreeTests.kt

@@ -25,6 +25,7 @@ import org.jetbrains.kotlinx.dataframe.api.asDataFrame
 import org.jetbrains.kotlinx.dataframe.api.asFrame
 import org.jetbrains.kotlinx.dataframe.api.asGroupBy
 import org.jetbrains.kotlinx.dataframe.api.at
+import org.jetbrains.kotlinx.dataframe.api.before
 import org.jetbrains.kotlinx.dataframe.api.by
 import org.jetbrains.kotlinx.dataframe.api.cast
 import org.jetbrains.kotlinx.dataframe.api.colsOf
@@ -702,6 +703,22 @@ class DataFrameTreeTests : BaseTest() {
         typed2.insert(colName) { nameAndCity.name.reversed() }.after { nameAndCity.name }.check()
     }
 
+    @Test
+    fun `insert column before`() {
+        val colName = "reversed"
+
+        fun DataFrame<GroupedPerson>.check() {
+            nameAndCity.columnsCount() shouldBe 3
+            nameAndCity.columnNames() shouldBe listOf(
+                typed2.nameAndCity.name.name(),
+                colName,
+                typed2.nameAndCity.city.name(),
+            )
+        }
+
+        typed2.insert(colName) { nameAndCity.name.reversed() }.before { nameAndCity.city }.check()
+    }
+
     @Test
     fun append() {
         val res = typed2.append(listOf("Bill", "San Francisco"), null, 66)