diff --git a/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/SizeTest.php b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/SizeTest.php
new file mode 100644
index 000000000..6a3c50649
--- /dev/null
+++ b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/SizeTest.php
@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Tests\Integration\Row\Reference\Expression;
+
+use function Flow\ETL\DSL\ref;
+use Flow\ETL\DSL\From;
+use Flow\ETL\DSL\To;
+use Flow\ETL\Exception\RuntimeException;
+use Flow\ETL\Flow;
+use Flow\ETL\Memory\ArrayMemory;
+use PHPUnit\Framework\TestCase;
+
+final class SizeTest extends TestCase
+{
+    public function test_size_on_array() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['array' => [1, 2, 3]],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('size', ref('array')->size())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['array' => [1, 2, 3], 'size' => 3],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_size_on_non_string_key() : void
+    {
+        $this->expectException(RuntimeException::class);
+
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => 1],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('size', ref('id')->size())
+            ->run();
+    }
+
+    public function test_size_on_string() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => 'value'],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('size', ref('key')->size())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => 'value', 'size' => 5],
+            ],
+            $memory->data
+        );
+    }
+}
diff --git a/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/SprintfTest.php b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/SprintfTest.php
new file mode 100644
index 000000000..94c953d0b
--- /dev/null
+++ b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/SprintfTest.php
@@ -0,0 +1,91 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Tests\Integration\Row\Reference\Expression;
+
+use function Flow\ETL\DSL\lit;
+use function Flow\ETL\DSL\ref;
+use Flow\ETL\DSL\From;
+use Flow\ETL\DSL\To;
+use Flow\ETL\Flow;
+use Flow\ETL\Memory\ArrayMemory;
+use PHPUnit\Framework\TestCase;
+
+final class SprintfTest extends TestCase
+{
+    public function test_sprintf() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => 'test %s'],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('sprintf', ref('key')->sprintf(lit('value')))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => 'test %s', 'sprintf' => 'test value'],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_sprintf_on_non_string_key() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => 1],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('sprintf', ref('id')->sprintf(lit('1')))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['id' => 1, 'sprintf' => null],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_sprintf_on_null_value() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => '1'],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('sprintf', ref('id')->sprintf(lit(null)))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['id' => '1', 'sprintf' => null],
+            ],
+            $memory->data
+        );
+    }
+}
diff --git a/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/StrPadTest.php b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/StrPadTest.php
new file mode 100644
index 000000000..201fec189
--- /dev/null
+++ b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/StrPadTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Tests\Integration\Row\Reference\Expression;
+
+use function Flow\ETL\DSL\ref;
+use Flow\ETL\DSL\From;
+use Flow\ETL\DSL\To;
+use Flow\ETL\Flow;
+use Flow\ETL\Memory\ArrayMemory;
+use PHPUnit\Framework\TestCase;
+
+final class StrPadTest extends TestCase
+{
+    public function test_strpad() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => 'value'],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('strpad', ref('key')->strPad(10, '*'))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => 'value', 'strpad' => 'value*****'],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_strpad_on_non_string_key() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => 1],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('strpad', ref('id')->strPad(10))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['id' => 1, 'strpad' => null],
+            ],
+            $memory->data
+        );
+    }
+}
diff --git a/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/StrReplaceTest.php b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/StrReplaceTest.php
new file mode 100644
index 000000000..9ff71f03d
--- /dev/null
+++ b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/StrReplaceTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Tests\Integration\Row\Reference\Expression;
+
+use function Flow\ETL\DSL\ref;
+use Flow\ETL\DSL\From;
+use Flow\ETL\DSL\To;
+use Flow\ETL\Flow;
+use Flow\ETL\Memory\ArrayMemory;
+use PHPUnit\Framework\TestCase;
+
+final class StrReplaceTest extends TestCase
+{
+    public function test_str_replace() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => 'value'],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('str_replace', ref('key')->strReplace('e', 'es'))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => 'value', 'str_replace' => 'values'],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_str_replace_on_non_string_key() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => 1],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('str_replace', ref('id')->strReplace('', ''))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['id' => 1, 'str_replace' => null],
+            ],
+            $memory->data
+        );
+    }
+}
diff --git a/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/ToLowerTest.php b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/ToLowerTest.php
new file mode 100644
index 000000000..86df3f468
--- /dev/null
+++ b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/ToLowerTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Tests\Integration\Row\Reference\Expression;
+
+use function Flow\ETL\DSL\ref;
+use Flow\ETL\DSL\From;
+use Flow\ETL\DSL\To;
+use Flow\ETL\Flow;
+use Flow\ETL\Memory\ArrayMemory;
+use PHPUnit\Framework\TestCase;
+
+final class ToLowerTest extends TestCase
+{
+    public function test_to_lower() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => 'VALUE'],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('to_lower', ref('key')->lower())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => 'VALUE', 'to_lower' => 'value'],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_to_lower_on_non_string_key() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => 1],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('to_lower', ref('id')->lower())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['id' => 1, 'to_lower' => 1],
+            ],
+            $memory->data
+        );
+    }
+}
diff --git a/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/ToUpperTest.php b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/ToUpperTest.php
new file mode 100644
index 000000000..8a94f5964
--- /dev/null
+++ b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/ToUpperTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Tests\Integration\Row\Reference\Expression;
+
+use function Flow\ETL\DSL\ref;
+use Flow\ETL\DSL\From;
+use Flow\ETL\DSL\To;
+use Flow\ETL\Flow;
+use Flow\ETL\Memory\ArrayMemory;
+use PHPUnit\Framework\TestCase;
+
+final class ToUpperTest extends TestCase
+{
+    public function test_to_upper() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => 'value'],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('to_upper', ref('key')->upper())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => 'value', 'to_upper' => 'VALUE'],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_to_upper_on_non_string_key() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => 1],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('to_upper', ref('id')->upper())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['id' => 1, 'to_upper' => 1],
+            ],
+            $memory->data
+        );
+    }
+}
diff --git a/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/TrimTest.php b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/TrimTest.php
new file mode 100644
index 000000000..54d3089e6
--- /dev/null
+++ b/src/core/etl/tests/Flow/ETL/Tests/Integration/Row/Reference/Expression/TrimTest.php
@@ -0,0 +1,141 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Tests\Integration\Row\Reference\Expression;
+
+use function Flow\ETL\DSL\ref;
+use Flow\ETL\DSL\From;
+use Flow\ETL\DSL\To;
+use Flow\ETL\Flow;
+use Flow\ETL\Memory\ArrayMemory;
+use Flow\ETL\Row\Reference\Expression\Trim\Type;
+use PHPUnit\Framework\TestCase;
+
+final class TrimTest extends TestCase
+{
+    public function test_trim_both() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => ' value '],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('trim', ref('key')->trim())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => ' value ', 'trim' => 'value'],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_trim_custom_characters() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => '-value '],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('trim', ref('key')->trim(characters: '-'))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => '-value ', 'trim' => 'value '],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_trim_left() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => ' value '],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('trim', ref('key')->trim(Type::LEFT))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => ' value ', 'trim' => 'value '],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_trim_on_non_string_key() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['id' => 1],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('trim', ref('id')->trim())
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['id' => 1, 'trim' => null],
+            ],
+            $memory->data
+        );
+    }
+
+    public function test_trim_right() : void
+    {
+        (new Flow())
+            ->read(
+                From::array(
+                    [
+                        ['key' => ' value '],
+                    ]
+                )
+            )
+            ->withEntry('row', ref('row')->unpack())
+            ->renameAll('row.', '')
+            ->drop('row')
+            ->withEntry('trim', ref('key')->trim(Type::RIGHT))
+            ->write(To::memory($memory = new ArrayMemory()))
+            ->run();
+
+        $this->assertSame(
+            [
+                ['key' => ' value ', 'trim' => ' value'],
+            ],
+            $memory->data
+        );
+    }
+}