CliBuilder not getting entire list of arguments for an option - groovy

Question

Problem
I need to parse command like:
groovy App.groovy --sourceFiles a.xlsx b.xlsx --destinationFolder ../legacy-data-migration
What I have tried
I write a CommandLineUtils, defined to be:
package com.signaturemd.sposZohoMergeScript.utils
import org.apache.commons.cli.Option
import org.apache.commons.cli.Options
import groovy.cli.commons.CliBuilder
import groovy.cli.commons.OptionAccessor
public final class CommandLineUtils {
private static CliBuilder cli;
public static CliBuilder GetCliBuilder() {
if (this.cli == null)
this.cli = new CliBuilder();
return this.cli;
}
public static OptionAccessor HandleAppCliInput(String[] args) {
return this.HandleCommandLineInput(args,
{ CliBuilder builder ->
builder.usage = "groovy App.groovy [OPTIONS]"
builder.header = "Merge multiple Excel files into a single file."
builder.footer = "Source files must be in XLSX format and destination folder must exist."
// Define options
builder << Option.builder()
.option("h")
.longOpt("help")
.desc("Print this help message.")
.build();
builder << Option.builder()
.option("s")
.longOpt("sourceFiles")
.desc("The source XLSX files to merge.")
.hasArgs()
.required()
.build();
builder << Option.builder()
.option("d")
.longOpt("destinationFolder")
.desc("The destination folder for the merged file.")
.numberOfArgs(1)
.required()
.build();
},
{ OptionAccessor options ->
// return (options.sourceFiles != null) && (!((List<String>)options.sourceFiles).isEmpty()) &&
return (options.sourceFiles) &&
(options.destinationFolder);
})
}
public static OptionAccessor HandleCommandLineInput(String[] args, Closure onGetSetup, Closure<Boolean> onValidateOptions) {
this.GetCliBuilder().with(onGetSetup);
OptionAccessor options = this.GetCliBuilder().parse(args);
if (!onValidateOptions(options)) {
printUsage();
System.exit(1);
}
return options;
}
public static void printUsage() {
println cli.usage();
}
}
Test
I write a JUnit test against the CommandLineUtils.HandleAppCliInput(), defined to be :
#Test
void testHandleAppCliInput() {
final String destinationFolder = "../legacy-data-migration";
final List<String> excelFiles = ["a.xlsx", "b.xlsx"];
final String[] commandTokens = "groovy App.groovy --sourceFiles ${excelFiles.join(' ')} --destinationFolder ${destinationFolder}"
.split(' ');
final String[] args = commandTokens.takeRight(commandTokens.length - 2);
assertTrue(args[0].equals("--sourceFiles"))
final OptionAccessor options = CommandLineUtils.HandleAppCliInput(args);
assertIterableEquals(excelFiles, options.sourceFiles);
assertEquals(destinationFolder, options.destinationFolder);
}
and it fails!
At run time, options.sourceFiles.equals("a.xlsx"), instead of the ['a.xlsx', 'b.xlsx'] that we're expecting...
What am I doing wrong here?
DISCLAIMER: I am using implementation 'org.apache.groovy:groovy-cli-commons:4.0.9'