diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 06364de3ef..f0d11195b3 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -247,10 +247,21 @@ jobs:
         env:
           PHP_CODESNIFFER_CBF: '1'
 
+      - name: "Install bashunit"
+        if: ${{ matrix.custom_ini == false && matrix.os == 'ubuntu-latest' }}
+        run: |
+          curl -s https://bashunit.typeddevs.com/install.sh > install.sh
+          chmod +x install.sh
+          ./install.sh
+
+      - name: "Run bashunit tests"
+        if: ${{ matrix.custom_ini == false && matrix.os == 'ubuntu-latest' }}
+        run: "./lib/bashunit -p tests/EndToEnd"
+
       # Note: The code style check is run multiple times against every PHP version
       # as it also acts as an integration test.
       - name: 'PHPCS: check code style without cache, no parallel'
-        if: ${{ matrix.custom_ini == false }}
+        if: ${{ matrix.custom_ini == false && matrix.os == 'windows-latest' }}
         run: php "bin/phpcs" --no-cache --parallel=1
 
       - name: Download the PHPCS phar
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
index 0fd2f38d0f..6285d269f1 100644
--- a/phpcs.xml.dist
+++ b/phpcs.xml.dist
@@ -11,6 +11,7 @@
     <exclude-pattern>*/src/Standards/*/Tests/*\.(inc|css|js)$</exclude-pattern>
     <exclude-pattern>*/tests/Core/*/*\.(inc|css|js)$</exclude-pattern>
     <exclude-pattern>*/tests/Core/*/Fixtures/*\.php$</exclude-pattern>
+    <exclude-pattern>*/tests/EndToEnd/Files/*\.inc$</exclude-pattern>
 
     <arg name="basepath" value="."/>
     <arg name="colors"/>
diff --git a/src/Runner.php b/src/Runner.php
index d527ea575e..37c3c65c7a 100644
--- a/src/Runner.php
+++ b/src/Runner.php
@@ -764,7 +764,7 @@ public function processFile($file)
      * The reporting information returned by each child process is merged
      * into the main reporter class.
      *
-     * @param array $childProcs An array of child processes to wait for.
+     * @param array<non-negative-int, non-empty-string> $childProcs An array of child processes to wait for.
      *
      * @return bool
      */
@@ -777,7 +777,8 @@ private function processChildProcs($childProcs)
 
         while (count($childProcs) > 0) {
             $pid = pcntl_waitpid(0, $status);
-            if ($pid <= 0) {
+            if ($pid <= 0 || isset($childProcs[$pid]) === false) {
+                // No child or a child with an unmanaged PID was returned.
                 continue;
             }
 
diff --git a/tests/EndToEnd/Files/.gitignore b/tests/EndToEnd/Files/.gitignore
new file mode 100644
index 0000000000..862bc749ba
--- /dev/null
+++ b/tests/EndToEnd/Files/.gitignore
@@ -0,0 +1 @@
+*.fixed
\ No newline at end of file
diff --git a/tests/EndToEnd/Files/ClassOneWithoutStyleError.inc b/tests/EndToEnd/Files/ClassOneWithoutStyleError.inc
new file mode 100644
index 0000000000..5ae6ac8f94
--- /dev/null
+++ b/tests/EndToEnd/Files/ClassOneWithoutStyleError.inc
@@ -0,0 +1,18 @@
+<?php
+
+/**
+ * Class containing no style errors according to the end-to-end tests phpcs.xml.dist.
+ *
+ * @copyright 2025 PHPCSStandards and contributors
+ * @license   https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/master/licence.txt BSD Licence
+ */
+
+namespace PHP_CodeSniffer\Tests\EndToEnd\Files;
+
+class ClassOneWithoutStyleError
+{
+    private function foo()
+    {
+        return 'bar';
+    }
+}
diff --git a/tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc b/tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc
new file mode 100644
index 0000000000..1fdc5b3b0b
--- /dev/null
+++ b/tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc
@@ -0,0 +1,20 @@
+<?php
+
+/**
+ * Class containing no style errors.
+ *
+ * @copyright 2025 PHPCSStandards and contributors
+ * @license   https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/master/licence.txt BSD Licence
+ */
+
+namespace PHP_CodeSniffer\Tests\EndToEnd\Files;
+
+class ClassTwoWithoutStyleError
+{
+    /**
+     * A property.
+     *
+     * @var string
+     */
+    private $bar = 'baz';
+}
diff --git a/tests/EndToEnd/Files/ClassWithStyleError.inc b/tests/EndToEnd/Files/ClassWithStyleError.inc
new file mode 100644
index 0000000000..4179ecdca1
--- /dev/null
+++ b/tests/EndToEnd/Files/ClassWithStyleError.inc
@@ -0,0 +1,22 @@
+<?php
+
+/**
+ * Class containing a simple style error that phpcbf can fix.
+ *
+ * @copyright 2025 PHPCSStandards and contributors
+ * @license   https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/master/licence.txt BSD Licence
+ */
+
+namespace PHP_CodeSniffer\Tests\EndToEnd\Files;
+
+class ClassWithStyleError
+{
+    /**
+     * The bracket for this function is misaligned and this can be automatically fixed by phpcbf.
+     *
+     * @return string
+     */
+    private function foo() {
+        return 'bar';
+    }
+}
diff --git a/tests/EndToEnd/Files/phpcs.xml.dist b/tests/EndToEnd/Files/phpcs.xml.dist
new file mode 100644
index 0000000000..0a10053386
--- /dev/null
+++ b/tests/EndToEnd/Files/phpcs.xml.dist
@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+<ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="PHP_CodeSniffer" xsi:noNamespaceSchemaLocation="phpcs.xsd">
+    <description>The coding standard for end to end tests.</description>
+
+    <rule ref="PSR12"/>
+
+    <file>.</file>
+
+    <arg name="basepath" value="."/>
+    <arg name="colors"/>
+    <arg name="parallel" value="75"/>
+    <arg value="p"/>
+</ruleset>
diff --git a/tests/EndToEnd/phpcbf_test.sh b/tests/EndToEnd/phpcbf_test.sh
new file mode 100644
index 0000000000..74780570b9
--- /dev/null
+++ b/tests/EndToEnd/phpcbf_test.sh
@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+function tear_down() {
+  rm -r tests/EndToEnd/Files/*.fixed
+}
+
+function test_phpcbf_is_working() {
+  OUTPUT="$(bin/phpcbf --no-cache --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc)"
+
+  assert_successful_code
+  assert_contains "No violations were found" "$OUTPUT"
+}
+
+function test_phpcbf_is_working_in_parallel() {
+  OUTPUT="$(bin/phpcbf --no-cache --parallel=2 --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc)"
+
+  assert_successful_code
+  assert_contains "No violations were found" "$OUTPUT"
+}
+
+function test_phpcbf_returns_error_on_issues() {
+  OUTPUT="$(bin/phpcbf --no-colors --no-cache --suffix=.fixed --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassWithStyleError.inc)"
+  assert_exit_code 1
+
+  assert_contains "F 1 / 1 (100%)" "$OUTPUT"
+  assert_contains "A TOTAL OF 1 ERROR WERE FIXED IN 1 FILE" "$OUTPUT"
+}
+
+function test_phpcbf_bug_1112() {
+  # See https://github.com/PHPCSStandards/PHP_CodeSniffer/issues/1112
+  if [[ "$(uname)" == "Darwin" ]]; then
+    # Perform some magic with `& fg` to prevent the processes from turning into a background job.
+    assert_successful_code "$(bash -ic 'bash --init-file <(echo "echo \"Subprocess\"") -c "bin/phpcbf --no-cache --parallel=2 --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc" & fg')"
+  else
+    # This is not needed on Linux / GitHub Actions
+    assert_successful_code "$(bash -ic 'bash --init-file <(echo "echo \"Subprocess\"") -c "bin/phpcbf --no-cache --parallel=2 --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc"')"
+  fi
+}
diff --git a/tests/EndToEnd/phpcs_test.sh b/tests/EndToEnd/phpcs_test.sh
new file mode 100644
index 0000000000..ef4aef8e36
--- /dev/null
+++ b/tests/EndToEnd/phpcs_test.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+function test_phpcs_is_working() {
+  assert_successful_code "$(bin/phpcs --no-cache --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc)"
+}
+
+function test_phpcs_is_working_in_parallel() {
+  assert_successful_code "$(bin/phpcs --no-cache --parallel=2 --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc)"
+}
+
+function test_phpcs_returns_error_on_issues() {
+  OUTPUT="$(bin/phpcs --no-colors --no-cache --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassWithStyleError.inc)"
+  assert_exit_code 2
+
+  assert_contains "E 1 / 1 (100%)" "$OUTPUT"
+  assert_contains "FOUND 1 ERROR AFFECTING 1 LINE" "$OUTPUT"
+}
+
+function test_phpcs_bug_1112() {
+  # See https://github.com/PHPCSStandards/PHP_CodeSniffer/issues/1112
+    if [[ "$(uname)" == "Darwin" ]]; then
+      # Perform some magic with `& fg` to prevent the processes from turning into a background job.
+      assert_successful_code "$(bash -ic 'bash --init-file <(echo "echo \"Subprocess\"") -c "bin/phpcs --no-cache --parallel=2 --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc" & fg')"
+    else
+      # This is not needed on Linux / GitHub Actions
+      assert_successful_code "$(bash -ic 'bash --init-file <(echo "echo \"Subprocess\"") -c "bin/phpcs --no-cache --parallel=2 --standard=tests/EndToEnd/Files/phpcs.xml.dist tests/EndToEnd/Files/ClassOneWithoutStyleError.inc tests/EndToEnd/Files/ClassTwoWithoutStyleError.inc"')"
+    fi
+}