diff --git a/tests/Spout/Writer/Common/Creator/StyleBuilderTest.php b/tests/Spout/Writer/Common/Creator/StyleBuilderTest.php
index afa1a72..7790928 100644
--- a/tests/Spout/Writer/Common/Creator/StyleBuilderTest.php
+++ b/tests/Spout/Writer/Common/Creator/StyleBuilderTest.php
@@ -41,4 +41,24 @@ class StyleBuilderTest extends TestCase
         $this->assertInstanceOf(Border::class, $baseStyle->getBorder(), 'Base style has a border');
         $this->assertInstanceOf(Border::class, $mergedStyle->getBorder(), 'Merged style has a border');
     }
+
+    /**
+     * @return void
+     */
+    public function testStyleBuilderShouldMergeFormats()
+    {
+        $baseStyle = (new StyleBuilder())
+            ->setFontBold()
+            ->setFormat('0.00')
+            ->build();
+
+        $currentStyle = (new StyleBuilder())->build();
+
+        $styleMerger = new StyleMerger();
+        $mergedStyle = $styleMerger->merge($currentStyle, $baseStyle);
+
+        $this->assertNull($currentStyle->getFormat(), 'Current style has no border');
+        $this->assertEquals('0.00', $baseStyle->getFormat(), 'Base style has a format 0.00');
+        $this->assertEquals('0.00', $mergedStyle->getFormat(), 'Merged style has a format 0.00');
+    }
 }
diff --git a/tests/Spout/Writer/XLSX/Manager/Style/StyleRegistryTest.php b/tests/Spout/Writer/XLSX/Manager/Style/StyleRegistryTest.php
index 6478a7c..6934081 100644
--- a/tests/Spout/Writer/XLSX/Manager/Style/StyleRegistryTest.php
+++ b/tests/Spout/Writer/XLSX/Manager/Style/StyleRegistryTest.php
@@ -74,4 +74,34 @@ class StyleRegistryTest extends TestCase
         $this->assertEquals(2, $styleRegistry->getBorderIdForStyleId($styleBoderRightBold->getId()), 'Style with border already set should have the same index');
         $this->assertEquals(0, $styleRegistry->getBorderIdForStyleId($styleNoBorder->getId()), 'Style with no border should have index 0');
     }
+
+    /**
+     * @return void
+     */
+    public function testRegisterStyleAlsoRegistersFormats()
+    {
+        $styleRegistry = $this->getStyleRegistry();
+
+        $styleBuiltinFormat = (new StyleBuilder())
+            ->setFontBold()
+            ->setFormat('0.00')//Builtin format
+            ->build();
+
+        $styleUserFormat = (new StyleBuilder())
+            ->setFontBold()
+            ->setFormat('0.000')
+            ->build();
+        $styleNoFormat = (new StyleBuilder())->setFontItalic()->build();
+
+        $styleRegistry->registerStyle($styleBuiltinFormat);
+        $styleRegistry->registerStyle($styleUserFormat);
+        $styleRegistry->registerStyle($styleNoFormat);
+
+        $this->assertCount(2, $styleRegistry->getRegisteredFormats(), 'There should be 2 registered formats');
+
+        $this->assertEquals(2, $styleRegistry->getFormatIdForStyleId($styleBuiltinFormat->getId()), 'First style with builtin format set should have index 2 (0 is for the default style)');
+        $this->assertEquals(164, $styleRegistry->getFormatIdForStyleId($styleUserFormat->getId()), 'Second style with user format set should have index 164 (0 is for the default style)');
+
+        $this->assertEquals(0, $styleRegistry->getFormatIdForStyleId($styleNoFormat->getId()), 'Style with no format should have index 0');
+    }
 }
diff --git a/tests/Spout/Writer/XLSX/WriterWithStyleTest.php b/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
index 83d2555..d556623 100644
--- a/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
+++ b/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
@@ -236,7 +236,7 @@ class WriterWithStyleTest extends TestCase
         $this->assertEquals(
             1,
             $formatsDomElement->getAttribute('count'),
-            'There should be 2 formats, including the 1 default ones'
+            'There should be 2 formats, including the default one'
         );
 
         $cellXfsDomElement = $this->getXmlSectionFromStylesXmlFile($fileName, 'cellXfs');