diff --git a/core/modules/migrate/tests/src/Kernel/process/HandleMultiplesTest.php b/core/modules/migrate/tests/src/Kernel/process/HandleMultiplesTest.php
index a56fe88..b4cc0e8 100644
--- a/core/modules/migrate/tests/src/Kernel/process/HandleMultiplesTest.php
+++ b/core/modules/migrate/tests/src/Kernel/process/HandleMultiplesTest.php
@@ -34,31 +34,39 @@ public function getDefinition() {
         ],
       ],
       'process' => [
+        // Process pipeline for testing values from string to array to string.
         'first' => [
+          // Expects a string and returns an array.
           [
             'plugin' => 'explode',
             'source' => 'scalar',
             'delimiter' => '/',
           ],
+          // Expects an array and returns a string.
           [
             'plugin' => 'extract',
             'index' => [1],
           ],
+          // Expects a string and returns a string.
           [
             'plugin' => 'callback',
             'callable' => 'strtoupper',
           ],
         ],
+        // Process pipeline for testing values from array to string to array.
         'second' => [
+          // Expects an array and returns a string.
           [
             'plugin' => 'extract',
             'source' => 'multiple',
             'index' => [1],
           ],
+          // Expects a string and returns a string.
           [
             'plugin' => 'callback',
             'callable' => 'strtoupper',
           ],
+          // Expects a string and returns an array.
           [
             'plugin' => 'explode',
             'delimiter' => '/',
@@ -106,14 +114,18 @@ public function scalarAndMultipleValuesProviderSource() {
       [
         'source_data' => [
           'id' => '1',
+          // Source value for the first pipeline.
           'scalar' => 'foo/bar',
+          // Source value for the second pipeline.
           'multiple' => [
             'foo',
             'bar/baz',
           ],
         ],
         'expected_data' => [
+          // Expected value from the first pipeline.
           'first' => 'BAR',
+          // Expected value from the second pipeline.
           'second' => [
             'BAR',
             'BAZ',