diff --git a/tests/LessRulesetTest.php b/tests/LessRulesetTest.php
new file mode 100644
index 00000000..1f56c1cf
--- /dev/null
+++ b/tests/LessRulesetTest.php
@@ -0,0 +1,112 @@
+<?php
+
+namespace ipl\Tests\Web;
+
+use ErrorException;
+use ipl\Tests\Web\Lib\LessRulesetWithTestableRenderCss;
+use ipl\Web\LessRuleset;
+
+class LessRulesetTest extends TestCase
+{
+    public function testSetWithSelectorIsCorrectlyRendered()
+    {
+        $set = LessRulesetWithTestableRenderCss::create('.foo', ['width' => 'auto']);
+
+        $this->assertSame('.foo', $set->getSelector());
+        $this->assertSame(
+            <<<'EOT'
+.foo {
+width: auto;
+}
+EOT
+            ,
+            $set->renderCss()
+        );
+    }
+
+    public function testSetWithoutSelectorIsCorrectlyRendered()
+    {
+        $set = new LessRulesetWithTestableRenderCss();
+        $set->setProperties(['width' => 'auto', 'height' => 'auto']);
+
+        $this->assertSame(['width' => 'auto', 'height' => 'auto'], $set->getProperties());
+        $this->assertSame(
+            <<<'EOT'
+width: auto;
+height: auto;
+EOT
+            ,
+            $set->renderCss()
+        );
+    }
+
+    public function testNestedSetsAreCorrectlyRendered()
+    {
+        $set = LessRulesetWithTestableRenderCss::create('.level1', ['width' => 'auto']);
+        $set->addRuleset(
+            LessRulesetWithTestableRenderCss::create('.level2', ['width' => '2em'])
+                ->add('.level3', ['width' => '1em'])
+        );
+
+        $this->assertSame(
+            <<<'EOT'
+.level1 {
+width: auto;
+.level2 {
+width: 2em;
+.level3 {
+width: 1em;
+}
+}
+}
+EOT
+            ,
+            $set->renderCss()
+        );
+    }
+
+    public function testSetsCanBeAdjustedAfterCreation()
+    {
+        $set = LessRulesetWithTestableRenderCss::create('.foo', ['width' => 'auto']);
+        $set->setProperty('line-height', 1.5);
+        $set['color'] = '#abc';
+
+        $this->assertSame('#abc', $set['color']);
+        $this->assertSame('1.5', $set->getProperty('line-height'));
+        $this->assertSame(
+            <<<'EOT'
+.foo {
+width: auto;
+line-height: 1.5;
+color: #abc;
+}
+EOT
+            ,
+            $set->renderCss()
+        );
+    }
+
+    public function testAccessingAMissingPropertyThrowsIfGetPropertyIsUsed()
+    {
+        $set = new LessRuleset();
+
+        try {
+            $set->getProperty('missing');
+        } catch (ErrorException $_) {
+            // $this->expectException() didn't work on GitHub for an unknown reason
+            $this->assertTrue(true);
+        }
+    }
+
+    public function testAccessingAMissingPropertyThrowsIfOffsetAccessIsUsed()
+    {
+        $set = new LessRuleset();
+
+        try {
+            $set['missing'];
+        } catch (ErrorException $_) {
+            // $this->expectException() didn't work on GitHub for an unknown reason
+            $this->assertTrue(true);
+        }
+    }
+}
diff --git a/tests/Lib/LessRulesetWithTestableRenderCss.php b/tests/Lib/LessRulesetWithTestableRenderCss.php
new file mode 100644
index 00000000..773ba71d
--- /dev/null
+++ b/tests/Lib/LessRulesetWithTestableRenderCss.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace ipl\Tests\Web\Lib;
+
+use ipl\Web\LessRuleset;
+
+class LessRulesetWithTestableRenderCss extends LessRuleset
+{
+    use TestableRenderCss;
+}
diff --git a/tests/Lib/TestableRenderCss.php b/tests/Lib/TestableRenderCss.php
new file mode 100644
index 00000000..14e24a54
--- /dev/null
+++ b/tests/Lib/TestableRenderCss.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace ipl\Tests\Web\Lib;
+
+use ipl\Web\LessRuleset;
+
+trait TestableRenderCss
+{
+    public function renderCss(): string
+    {
+        return $this->renderLess();
+    }
+}