Add duplicate() function to Query Builder

Signed-off-by: davidarendsen <davidarendsen@hey.com>

tests/Functions/DuplicateFunctionTest.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Functions;
+
+use Arendsen\FluxQueryBuilder\Functions\Duplicate;
+use PHPUnit\Framework\TestCase;
+
+final class DuplicateFunctionTest extends TestCase
+{
+    public function testSimpleDuplicate()
+    {
+        $expression = new Duplicate('tag', 'tag_dup');
+
+        $query = '|> duplicate(column: "tag", as: "tag_dup") ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+}

tests/Generic/QueryBuilderTest.php

@@ -124,12 +124,14 @@ final class QueryBuilderTest extends TestCase
             ->addWindow('20s')
             ->addReduce(['count' => new MathType('accumulator.count + 1')], ['count' => 0])
             ->addMean()
+            ->addDuplicate('tag', 'tag_dup')
             ->addFilter(KeyValue::setGreaterOrEqualTo('count', 1)->andGreaterOrEqualTo('count2', 2))
             ->addUnWindow();
 
         $expectedQuery = 'from(bucket: "test_bucket") |> range(start: time(v: 2022-08-12T17:31:00Z)) ' .
         '|> reduce(fn: (r, accumulator) => ({count: accumulator.count + 1}), identity: {count: 0}) ' .
-        '|> window(every: 20s) |> mean() |> filter(fn: (r) => r._measurement == "test_measurement") ' .
+        '|> window(every: 20s) |> mean() |> duplicate(column: "tag", as: "tag_dup") ' .
+        '|> filter(fn: (r) => r._measurement == "test_measurement") ' .
         '|> filter(fn: (r) => r.count >= 1 and r.count2 >= 2) |> window(every: inf) ';
 
         $this->assertEquals($expectedQuery, $queryBuilder->build());