diff --git a/phpunit.xml b/phpunit.xml
index ff9ee7c..a917a30 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,5 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit bootstrap="vendor/autoload.php" colors="true">
+    <source>
+        <include>
+            <directory suffix=".php">src/</directory>
+        </include>
+    </source>
     <testsuites>
         <testsuite name="tests">
             <directory>test/tests/</directory>
diff --git a/src/Query/Generator/SQL.php b/src/Query/Generator/SQL.php
index 4f8e443..88f0fad 100644
--- a/src/Query/Generator/SQL.php
+++ b/src/Query/Generator/SQL.php
@@ -118,8 +118,12 @@ private function generateWhere(Query $query, WhereCondition|WhereGroup $where =
             $where = $query->getWhere();
         }
         if ($where instanceof WhereCondition) {
-            if ($where->value === null && $where->operator === "=") {
-                $where->operator = "IS";
+            if ($where->value === null) {
+                if ($where->operator === "=") {
+                    $where->operator = "IS";
+                } elseif ($where->operator === "!=") {
+                    $where->operator = "IS NOT";
+                }
             }
 
             $value = $where->value;
@@ -233,7 +237,7 @@ private function generateFields(Query $query): string
                 }
 
             } else if ($field instanceof UpdateField) {
-                $fieldStrings[] = $this->columnEnclosure . $field->key . $this->columnEnclosure . "=" . $this->generateValue($field->value);
+                $fieldStrings[] = $this->columnEnclosure . $field->key . $this->columnEnclosure . " = " . $this->generateValue($field->value);
             }
         }
 
diff --git a/src/Query/SelectQuery.php b/src/Query/SelectQuery.php
index 3f15748..c845c14 100644
--- a/src/Query/SelectQuery.php
+++ b/src/Query/SelectQuery.php
@@ -28,7 +28,7 @@ public function __construct(null|WhereCondition|array|WhereGroup $where = null,
                                 null|array                           $order = null,
                                 null|array                           $fields = null,
                                 null|Limit|array|int                 $limit = null,
-                                null|array $group = null)
+                                null|array                           $group = null)
     {
         if ($where) {
             $this->where($where);
diff --git a/test/tests/SQLTest.php b/test/tests/SQLTest.php
new file mode 100644
index 0000000..fa3cfc9
--- /dev/null
+++ b/test/tests/SQLTest.php
@@ -0,0 +1,287 @@
+<?php
+
+namespace Aternos\Model\Test\Tests;
+
+use Aternos\Model\Query\DeleteQuery;
+use Aternos\Model\Query\Generator\SQL;
+use Aternos\Model\Query\Limit;
+use Aternos\Model\Query\SelectField;
+use Aternos\Model\Query\SelectQuery;
+use Aternos\Model\Query\UpdateQuery;
+use Aternos\Model\Query\WhereCondition;
+use Aternos\Model\Query\WhereGroup;
+use Aternos\Model\Test\Src\TestModel;
+use PHPUnit\Framework\TestCase;
+
+class SQLTest extends TestCase
+{
+    protected SQL $sql;
+
+    protected function setUp(): void
+    {
+        $this->sql = new SQL("addslashes");
+    }
+
+    public function testSelect()
+    {
+        $query = new SelectQuery();
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereCondition()
+    {
+        $query = new SelectQuery(
+            new WhereCondition('text', 'value'),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`text` = 'value')", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereConditionNumber()
+    {
+        $query = new SelectQuery(
+            new WhereCondition('number', 1),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`number` = 1)", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereConditionFloat()
+    {
+        $query = new SelectQuery(
+            new WhereCondition('number', 1.5),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`number` = 1.5)", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereConditionOperator()
+    {
+        $query = new SelectQuery(
+            new WhereCondition('text', 'value', '!='),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`text` != 'value')", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereConditionNull()
+    {
+        $query = new SelectQuery(
+            new WhereCondition('text', null),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`text` IS NULL)", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereConditionNotNull()
+    {
+        $query = new SelectQuery(
+            new WhereCondition('text', null, '!='),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`text` IS NOT NULL)", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereConditionIN()
+    {
+        $query = new SelectQuery(
+            new WhereCondition('number', [1.5, 5, "a", ["b", "c", "d"]], 'IN'),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`number` IN (1.5, 5, 'a', ('b', 'c', 'd')))", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereArray()
+    {
+        $query = new SelectQuery([
+            'number' => 1,
+            'text' => 'value',
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`number` = 1 AND `text` = 'value')", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereArrayOperator()
+    {
+        $query = new SelectQuery([
+            ['number', 0.5],
+            ['number', '<', 1],
+            'text' => 'value',
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`number` = 0.5 AND `number` < 1 AND `text` = 'value')", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereGroup()
+    {
+        $query = new SelectQuery(
+            new WhereGroup([
+                new WhereCondition('number', 1, '<'),
+                new WhereCondition('number', 0, '>'),
+            ]),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`number` < 1 AND `number` > 0)", $this->sql->generate($query));
+    }
+
+    public function testSelectWhereGroupOR()
+    {
+        $query = new SelectQuery(
+            new WhereGroup([
+                new WhereCondition('number', 1, '>'),
+                new WhereCondition('number', 0, '<'),
+            ], WhereGroup::OR),
+        );
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` WHERE (`number` > 1 OR `number` < 0)", $this->sql->generate($query));
+    }
+
+    public function testSelectSingleField()
+    {
+        $query = new SelectQuery(fields: ['text']);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT `text` FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectSelectFields()
+    {
+        $query = new SelectQuery(fields: ['text', 'number']);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT `text`, `number` FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectOrder()
+    {
+        $query = new SelectQuery(order: [
+            'number' => 'ASC',
+            'text' => 'DESC',
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` ORDER BY `number` ASC, `text` DESC", $this->sql->generate($query));
+    }
+
+    public function testSelectCount()
+    {
+        $query = new SelectQuery(fields: [
+            (new SelectField('number'))->setFunction(SelectField::COUNT),
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT COUNT(`number`) FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectCountStar()
+    {
+        $query = new SelectQuery(fields: [
+            (new SelectField('*'))->setFunction(SelectField::COUNT),
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT COUNT(*) FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectSum()
+    {
+        $query = new SelectQuery(fields: [
+            (new SelectField('number'))->setFunction(SelectField::SUM),
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT SUM(`number`) FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectSumAs()
+    {
+        $query = new SelectQuery(fields: [
+            (new SelectField('number'))->setFunction(SelectField::SUM)->setAlias('sum'),
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT SUM(`number`) AS `sum` FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectAVG()
+    {
+        $query = new SelectQuery(fields: [
+            (new SelectField('number'))->setFunction(SelectField::AVERAGE),
+        ]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT AVG(`number`) FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testSelectLimitNumber()
+    {
+        $query = new SelectQuery(limit:100);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` LIMIT 0, 100", $this->sql->generate($query));
+    }
+
+    public function testSelectLimitArray()
+    {
+        $query = new SelectQuery(limit:[5, 100]);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` LIMIT 5, 100", $this->sql->generate($query));
+    }
+
+    public function testSelectLimit()
+    {
+        $query = new SelectQuery(limit:new Limit(100, 5));
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` LIMIT 5, 100", $this->sql->generate($query));
+    }
+
+    public function testSelectGroup()
+    {
+        $query = new SelectQuery(group:['number', 'text']);
+        $query->modelClassName = TestModel::class;
+
+        $this->assertEquals("SELECT * FROM `test` GROUP BY `number`, `text`", $this->sql->generate($query));
+    }
+
+    public function testDelete()
+    {
+        $query = new DeleteQuery();
+        $query->modelClassName = TestModel::class;
+
+        /** @noinspection SqlWithoutWhere */
+        $this->assertEquals("DELETE FROM `test`", $this->sql->generate($query));
+    }
+
+    public function testDeleteLimit()
+    {
+        $query = new DeleteQuery(limit: 100);
+        $query->modelClassName = TestModel::class;
+
+        /** @noinspection SqlWithoutWhere */
+        $this->assertEquals("DELETE FROM `test` LIMIT 100", $this->sql->generate($query));
+    }
+
+    public function testUpdate()
+    {
+        $query = new UpdateQuery(['text' => 'value']);
+        $query->modelClassName = TestModel::class;
+
+        /** @noinspection SqlWithoutWhere */
+        $this->assertEquals("UPDATE `test` SET `text` = 'value'", $this->sql->generate($query));
+    }
+}