diff --git a/core/lib/Drupal/Component/Gettext/PoHeader.php b/core/lib/Drupal/Component/Gettext/PoHeader.php
index 5dd13a5d5b9..96793b5e956 100644
--- a/core/lib/Drupal/Component/Gettext/PoHeader.php
+++ b/core/lib/Drupal/Component/Gettext/PoHeader.php
@@ -188,7 +188,7 @@ class PoHeader {
    *   - 'nplurals': The number of plural forms defined by the plural formula.
    *   - 'plurals': Array of plural positions keyed by plural value.
    *
-   * @throws Exception
+   * @throws \Exception
    */
   public function parsePluralForms($pluralforms) {
     $plurals = [];
@@ -473,7 +473,7 @@ class PoHeader {
    *   Number of the plural string to be used for the given plural value.
    *
    * @see parseArithmetic()
-   * @throws Exception
+   * @throws \Exception
    */
   protected function evaluatePlural($element_stack, $n) {
     $count = count($element_stack);
diff --git a/core/lib/Drupal/Component/Gettext/PoStreamReader.php b/core/lib/Drupal/Component/Gettext/PoStreamReader.php
index f84d2514c0c..9548ea7ea22 100644
--- a/core/lib/Drupal/Component/Gettext/PoStreamReader.php
+++ b/core/lib/Drupal/Component/Gettext/PoStreamReader.php
@@ -146,7 +146,7 @@ class PoStreamReader implements PoStreamInterface, PoReaderInterface {
    * Opens the stream and reads the header. The stream is ready for reading
    * items after.
    *
-   * @throws Exception
+   * @throws \Exception
    *   If the URI is not yet set.
    */
   public function open() {
@@ -162,7 +162,7 @@ class PoStreamReader implements PoStreamInterface, PoReaderInterface {
   /**
    * Implements Drupal\Component\Gettext\PoStreamInterface::close().
    *
-   * @throws Exception
+   * @throws \Exception
    *   If the stream is not open.
    */
   public function close() {
@@ -506,6 +506,8 @@ class PoStreamReader implements PoStreamInterface, PoReaderInterface {
       $this->_errors[] = SafeMarkup::format('The translation stream %uri ended unexpectedly at line %line.', $log_vars);
       return FALSE;
     }
+
+    return;
   }
 
   /**
diff --git a/core/lib/Drupal/Component/Gettext/PoStreamWriter.php b/core/lib/Drupal/Component/Gettext/PoStreamWriter.php
index 5419b210aaf..1e3f3871e39 100644
--- a/core/lib/Drupal/Component/Gettext/PoStreamWriter.php
+++ b/core/lib/Drupal/Component/Gettext/PoStreamWriter.php
@@ -81,7 +81,7 @@ class PoStreamWriter implements PoWriterInterface, PoStreamInterface {
   /**
    * Implements Drupal\Component\Gettext\PoStreamInterface::close().
    *
-   * @throws Exception
+   * @throws \Exception
    *   If the stream is not open.
    */
   public function close() {
@@ -89,7 +89,7 @@ class PoStreamWriter implements PoWriterInterface, PoStreamInterface {
       fclose($this->_fd);
     }
     else {
-      throw new Exception('Cannot close stream that is not open.');
+      throw new \Exception('Cannot close stream that is not open.');
     }
   }
 
@@ -100,13 +100,13 @@ class PoStreamWriter implements PoWriterInterface, PoStreamInterface {
    *   Piece of string to write to the stream. If the value is not directly a
    *   string, casting will happen in writing.
    *
-   * @throws Exception
+   * @throws \Exception
    *   If writing the data is not possible.
    */
   private function write($data) {
     $result = fwrite($this->_fd, $data);
-    if ($result === FALSE) {
-      throw new Exception('Unable to write data: ' . substr($data, 0, 20));
+    if ($result === FALSE || $result != strlen($data)) {
+      throw new \Exception('Unable to write data: ' . substr($data, 0, 20));
     }
   }
 
@@ -137,12 +137,12 @@ class PoStreamWriter implements PoWriterInterface, PoStreamInterface {
   /**
    * Implements Drupal\Component\Gettext\PoStreamInterface::getURI().
    *
-   * @throws Exception
+   * @throws \Exception
    *   If the URI is not set.
    */
   public function getURI() {
     if (empty($this->_uri)) {
-      throw new Exception('No URI set.');
+      throw new \Exception('No URI set.');
     }
     return $this->_uri;
   }
diff --git a/core/tests/Drupal/Tests/Component/Gettext/PoStreamWriterTest.php b/core/tests/Drupal/Tests/Component/Gettext/PoStreamWriterTest.php
new file mode 100644
index 00000000000..7f636c10866
--- /dev/null
+++ b/core/tests/Drupal/Tests/Component/Gettext/PoStreamWriterTest.php
@@ -0,0 +1,118 @@
+<?php
+
+namespace Drupal\Tests\Component\Gettext;
+
+use Drupal\Component\Gettext\PoItem;
+use Drupal\Component\Gettext\PoStreamWriter;
+use org\bovigo\vfs\vfsStream;
+use org\bovigo\vfs\vfsStreamFile;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Component\Gettext\PoStreamWriter
+ * @group Gettext
+ */
+class PoStreamWriterTest extends TestCase {
+
+  /**
+   * The PO writer object under test.
+   *
+   * @var \Drupal\Component\Gettext\PoStreamWriter
+   */
+  protected $poWriter;
+
+  /**
+   * The mock po file.
+   *
+   * @var \org\bovigo\vfs\vfsStreamFile
+   */
+  protected $poFile;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->poWriter = new PoStreamWriter();
+
+    $root = vfsStream::setup();
+    $this->poFile = new vfsStreamFile('powriter.po');
+    $root->addChild($this->poFile);
+  }
+
+  /**
+   * @covers ::getURI
+   */
+  public function testGetUriException() {
+    if (method_exists($this, 'expectException')) {
+      $this->expectException(\Exception::class, 'No URI set.');
+    }
+    else {
+      $this->setExpectedException(\Exception::class, 'No URI set.');
+    }
+
+    $this->poWriter->getURI();
+  }
+
+  /**
+   * @covers ::writeItem
+   * @dataProvider providerWriteData
+   */
+  public function testWriteItem($poContent, $expected, $long) {
+    if ($long) {
+      if (method_exists($this, 'expectException')) {
+        $this->expectException(\Exception::class, 'Unable to write data:');
+      }
+      else {
+        $this->setExpectedException(\Exception::class, 'Unable to write data:');
+      }
+    }
+
+    // Limit the file system quota to make the write fail on long strings.
+    vfsStream::setQuota(10);
+
+    $this->poWriter->setURI($this->poFile->url());
+    $this->poWriter->open();
+
+    $poItem = $this->prophesize(PoItem::class);
+    $poItem->__toString()->willReturn($poContent);
+
+    $this->poWriter->writeItem($poItem->reveal());
+    $this->poWriter->close();
+    $this->assertEquals(file_get_contents($this->poFile->url()), $expected);
+  }
+
+  /**
+   * @return array
+   *   - Content to write.
+   *   - Written content.
+   *   - Content longer than 10 bytes.
+   */
+  public function providerWriteData() {
+    return [
+      ['', '', FALSE],
+      ["\r\n", "\r\n", FALSE],
+      ['write this if you can', 'write this', TRUE],
+      ['éáíó>&', 'éáíó>&', FALSE],
+      ['éáíó>&<', 'éáíó>&', TRUE],
+      ['中文 890', '中文 890', FALSE],
+      ['中文 89012', '中文 890', TRUE],
+    ];
+  }
+
+  /**
+   * @covers ::close
+   */
+  public function testCloseException() {
+    if (method_exists($this, 'expectException')) {
+      $this->expectException(\Exception::class, 'Cannot close stream that is not open.');
+    }
+    else {
+      $this->setExpectedException(\Exception::class, 'Cannot close stream that is not open.');
+    }
+
+    $this->poWriter->close();
+  }
+
+}