Fix incorrect assertion in Java concat (#8258)

Fix #8246.

Authors:
  - Alfred Xu (https://github.com/sperlingxx)

Approvers:
  - Liangcai Li (https://github.com/firestarman)
  - Jason Lowe (https://github.com/jlowe)
  - Robert (Bobby) Evans (https://github.com/revans2)

URL: #8258

java/src/main/java/ai/rapids/cudf/ColumnVector.java

@@ -488,7 +488,7 @@ public static ColumnVector concatenate(ColumnView... columns) {
    * Concatenate columns of strings together, combining a corresponding row from each column
    * into a single string row of a new column with no separator string inserted between each
    * combined string and maintaining null values in combined rows.
-   * @param columns array of columns containing strings.
+   * @param columns array of columns containing strings, must be non-empty
    * @return A new java column vector containing the concatenated strings.
    */
   public static ColumnVector stringConcatenate(ColumnView[] columns) {
@@ -505,11 +505,12 @@ public static ColumnVector stringConcatenate(ColumnView[] columns) {
    * @param narep string scalar indicating null behavior. If set to null and any string in the row
    *              is null the resulting string will be null. If not null, null values in any column
    *              will be replaced by the specified string.
-   * @param columns array of columns containing strings, must be more than 2 columns
+   * @param columns array of columns containing strings, must be non-empty
    * @return A new java column vector containing the concatenated strings.
    */
   public static ColumnVector stringConcatenate(Scalar separator, Scalar narep, ColumnView[] columns) {
-    assert columns.length >= 2 : ".stringConcatenate() operation requires at least 2 columns";
+    assert columns != null : "input columns should not be null";
+    assert columns.length > 0 : "input columns should not be empty";
     assert separator != null : "separator scalar provided may not be null";
     assert separator.getType().equals(DType.STRING) : "separator scalar must be a string scalar";
     assert narep != null : "narep scalar provided may not be null";
@@ -529,7 +530,7 @@ public static ColumnVector stringConcatenate(Scalar separator, Scalar narep, Col
    * from each column into a single list row of a new column.
    * NOTICE: Any concatenation involving a null list element will result in a null list.
    *
-   * @param columns array of columns containing lists, must be more than 2 columns
+   * @param columns array of columns containing lists, must be non-empty
    * @return A new java column vector containing the concatenated lists.
    */
   public static ColumnVector listConcatenateByRow(ColumnView... columns) {
@@ -543,12 +544,12 @@ public static ColumnVector listConcatenateByRow(ColumnView... columns) {
    * @param ignoreNull whether to ignore null list element of input columns: If true, null list
    *                   will be ignored from concatenation; Otherwise, any concatenation involving
    *                   a null list element will result in a null list
-   * @param columns    array of columns containing lists, must be more than 2 columns
+   * @param columns    array of columns containing lists, must be non-empty
    * @return A new java column vector containing the concatenated lists.
    */
   public static ColumnVector listConcatenateByRow(boolean ignoreNull, ColumnView... columns) {
     assert columns != null : "input columns should not be null";
-    assert columns.length >= 2 : "listConcatenateByRow requires at least 2 columns";
+    assert columns.length > 0 : "input columns should not be empty";
 
     long[] columnViews = new long[columns.length];
     for(int i = 0; i < columns.length; i++) {

java/src/test/java/ai/rapids/cudf/ColumnVectorTest.java

@@ -2037,9 +2037,8 @@ void testStringConcat() {
       }
     });
     assertThrows(AssertionError.class, () -> {
-      try (ColumnVector sv = ColumnVector.fromStrings("a", "B", "cd");
-           Scalar emptyString = Scalar.fromString("");
-           ColumnVector concat = ColumnVector.stringConcatenate(emptyString, emptyString, new ColumnView[]{sv})) {
+      try (Scalar emptyString = Scalar.fromString("");
+           ColumnVector concat = ColumnVector.stringConcatenate(emptyString, emptyString, new ColumnView[]{})) {
       }
     });
     assertThrows(CudfException.class, () -> {
@@ -2085,6 +2084,16 @@ void testStringConcatWithNulls() {
          ColumnVector concat = ColumnVector.stringConcatenate(emptyString, nullSubstitute, new ColumnView[]{v, v})) {
       assertColumnsAreEqual(concat, e_concat);
     }
+
+    try (ColumnVector v = ColumnVector.fromStrings("a", "B", "cd", "\u0480\u0481", "E\tf",
+        "g\nH", "IJ\"\u0100\u0101\u0500\u0501",
+        "kl m", "Nop1", "\\qRs2", null,
+        "3tuV\'", "wX4Yz", "\ud720\ud721");
+         Scalar emptyString = Scalar.fromString("");
+         Scalar nullSubstitute = Scalar.fromString("NULL");
+         ColumnVector concat = ColumnVector.stringConcatenate(emptyString, nullSubstitute, new ColumnView[]{v})) {
+      assertColumnsAreEqual(v, concat);
+    }
   }
 
   @Test
@@ -2102,6 +2111,13 @@ void testStringConcatSeparators() {
 
   @Test
   void testListConcatByRow() {
+    try (ColumnVector cv = ColumnVector.fromLists(new HostColumnVector.ListType(true,
+            new HostColumnVector.BasicType(true, DType.INT32)),
+        Arrays.asList(0), Arrays.asList(1, 2, 3), null, Arrays.asList(), Arrays.asList());
+         ColumnVector result = ColumnVector.listConcatenateByRow(cv)) {
+      assertColumnsAreEqual(cv, result);
+    }
+
     try (ColumnVector cv1 = ColumnVector.fromLists(new HostColumnVector.ListType(true,
             new HostColumnVector.BasicType(true, DType.INT32)),
         Arrays.asList(0), Arrays.asList(1, 2, 3), null, Arrays.asList(), Arrays.asList());
@@ -2148,13 +2164,6 @@ void testListConcatByRow() {
       assertColumnsAreEqual(expect, result);
     }
 
-    assertThrows(AssertionError.class, () -> {
-      try (ColumnVector cv = ColumnVector.fromLists(new HostColumnVector.ListType(true,
-          new HostColumnVector.BasicType(true, DType.INT32)), Arrays.asList(1, 2, 3));
-           ColumnVector result = ColumnVector.listConcatenateByRow(cv)) {
-      }
-    });
-
     assertThrows(CudfException.class, () -> {
       try (ColumnVector cv = ColumnVector.fromInts(1, 2, 3);
            ColumnVector result = ColumnVector.listConcatenateByRow(cv, cv)) {
@@ -2190,6 +2199,13 @@ void testListConcatByRow() {
 
   @Test
   void testListConcatByRowIgnoreNull() {
+    try (ColumnVector cv = ColumnVector.fromLists(new HostColumnVector.ListType(true,
+            new HostColumnVector.BasicType(true, DType.INT32)),
+        Arrays.asList(0), Arrays.asList(1, 2, 3), null, Arrays.asList(), Arrays.asList());
+         ColumnVector result = ColumnVector.listConcatenateByRow(true, cv)) {
+      assertColumnsAreEqual(cv, result);
+    }
+
     try (ColumnVector cv1 = ColumnVector.fromLists(new HostColumnVector.ListType(true,
             new HostColumnVector.BasicType(true, DType.INT32)),
         Arrays.asList((Integer) null), Arrays.asList(1, 2, 3), null, Arrays.asList(), null);