Add KeyValue expression

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

tests/Expression/KeyValueTest.php

@@ -0,0 +1,22 @@
+<?php
+declare(strict_types=1);
+
+use Arendsen\FluxQueryBuilder\Expression\KeyValue;
+use PHPUnit\Framework\TestCase;
+
+final class KeyValueExpressionTest extends TestCase {
+
+    public function testSimpleKeyvalue()
+    {
+        $keyvalue = KeyValue::set('_measurement', 'test_measurement')
+            ->and('_field', 'user')
+            ->or('_field', 'field2')
+            ->and('user', 'my_username');
+
+        $query = 'r._measurement == "test_measurement" and r._field == "user" or ' . 
+            'r._field == "field2" and r.user == "my_username"';
+
+        $this->assertEquals($keyvalue->__toString(), $query);
+    }
+
+}

tests/Function/FilterFunctionTest.php

@@ -1,9 +1,7 @@
 <?php
 declare(strict_types=1);
 
-use Arendsen\FluxQueryBuilder\Expression\Filter\AndExpression;
-use Arendsen\FluxQueryBuilder\Expression\Filter\OrExpression;
-use Arendsen\FluxQueryBuilder\Expression\Filter\Measurement;
+use Arendsen\FluxQueryBuilder\Expression\KeyValue;
 use Arendsen\FluxQueryBuilder\Function\Filter;
 use PHPUnit\Framework\TestCase;
 
@@ -12,10 +10,10 @@ final class FilterFunctionTest extends TestCase {
     public function testSimpleFilter()
     {
         $expression = new Filter([
-            new Measurement('test_measurement'),
-            new AndExpression('_field', 'user'),
-            new OrExpression('_field', 'field2'),
-            'and r.user == "my_username"',
+            KeyValue::set('_measurement', 'test_measurement')
+                ->and('_field', 'user')
+                ->or('_field', 'field2')
+                ->and('user', 'my_username'),
         ]);
 
         $query = '|> filter(fn: (r) => r._measurement == "test_measurement" and r._field == "user" or ' . 

tests/Function/FromFunctionTest.php

@@ -4,7 +4,7 @@ declare(strict_types=1);
 use Arendsen\FluxQueryBuilder\Function\From;
 use PHPUnit\Framework\TestCase;
 
-final class FromExpressionTest extends TestCase {
+final class FromFunctionTest extends TestCase {
 
     /**
      * @dataProvider somethingProvider