diff --git a/features/behat-steps.feature b/features/behat-steps.feature
index b38eac4c..beaeaf5c 100644
--- a/features/behat-steps.feature
+++ b/features/behat-steps.feature
@@ -389,6 +389,19 @@ Feature: Test that WP-CLI Behat steps work as expected
       """
     Then the wp-cli.yml file should exist
     And the mock-requests.php file should exist
+    And the mock-requests-data.php file should exist
+
+    When I run `php -l mock-requests.php`
+    Then STDOUT should contain:
+      """
+      No syntax errors detected
+      """
+
+    When I run `php -l mock-requests-data.php`
+    Then STDOUT should contain:
+      """
+      No syntax errors detected
+      """
 
   @require-wp
   Scenario: Test background process launch
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
index 0aff9e2d..cad05419 100644
--- a/phpcs.xml.dist
+++ b/phpcs.xml.dist
@@ -98,4 +98,19 @@
 	<rule ref="WordPress.WP.GlobalVariablesOverride">
 		<exclude-pattern>*/generate-coverage\.php$</exclude-pattern>
 	</rule>
+
+	<!-- These are stand-alone files that are copied into the test run directory and
+		 executed by the child WP-CLI process, not loaded as part of this package.
+		 They declare a class once per supported Requests major version, and their
+		 method signatures are dictated by the transport interface they implement,
+		 so unused parameters cannot be dropped. -->
+	<rule ref="Generic.Files.OneObjectStructurePerFile">
+		<exclude-pattern>*/src/Context/templates/*</exclude-pattern>
+	</rule>
+	<rule ref="Generic.Classes.DuplicateClassName">
+		<exclude-pattern>*/src/Context/templates/*</exclude-pattern>
+	</rule>
+	<rule ref="Generic.CodeAnalysis.UnusedFunctionParameter">
+		<exclude-pattern>*/src/Context/templates/*</exclude-pattern>
+	</rule>
 </ruleset>
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index 427c1a52..50a31b50 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -7,6 +7,9 @@ parameters:
     - tests
   excludePaths:
     - tests/data
+    # Templates are copied into the test run directory and executed by the
+    # child WP-CLI process, where Requests v1 classes may still exist.
+    - src/Context/templates
   scanDirectories:
     - vendor/wp-cli/wp-cli
     - vendor/phpunit/php-code-coverage
diff --git a/src/Context/GivenStepDefinitions.php b/src/Context/GivenStepDefinitions.php
index baf92cf9..03a87493 100644
--- a/src/Context/GivenStepDefinitions.php
+++ b/src/Context/GivenStepDefinitions.php
@@ -191,6 +191,7 @@ public function given_a_request_to_a_url_respond_with_file( $url_or_pattern, PyS
 
 		$config_file = $this->variables['RUN_DIR'] . '/wp-cli.yml';
 		$mock_file   = $this->variables['RUN_DIR'] . '/mock-requests.php';
+		$data_file   = $this->variables['RUN_DIR'] . '/mock-requests-data.php';
 		$dir         = dirname( $config_file );
 
 		if ( ! file_exists( $dir ) ) {
@@ -209,146 +210,12 @@ public function given_a_request_to_a_url_respond_with_file( $url_or_pattern, PyS
 
 		$this->mocked_requests[ $url_or_pattern ] = (string) $content;
 
-		$mocked_requests = var_export( $this->mocked_requests, true /* return */ );
-
-		$mock_file_contents = <<<FILE
-<?php
-/**
- * HTTP request mocking supporting both Requests v1 and v2.
- */
-
-trait WP_CLI_Tests_Mock_Requests_Trait {
-	public function request( \$url, \$headers = array(), \$data = array(), \$options = array() ) {
-		\$mocked_requests = $mocked_requests;
-
-		foreach ( \$mocked_requests as \$pattern => \$response ) {
-			\$pattern = '/' . preg_quote( \$pattern, '/' ) . '/';
-			if ( 1 === preg_match( \$pattern, \$url ) ) {
-				\$pos = strpos( \$response, "\\n\\n");
-				if ( false !== \$pos ) {
-					\$response = substr( \$response, 0, \$pos ) . "\\r\\n\\r\\n" . substr( \$response, \$pos + 2 );
-				}
-				if ( ! empty( \$options['filename'] ) ) {
-					\$body = '';
-					\$body_pos = strpos( \$response, "\\r\\n\\r\\n" );
-					if ( false !== \$body_pos ) {
-						\$body = substr( \$response, \$body_pos + 4 );
-					}
-					file_put_contents( \$options['filename'], \$body );
-				}
-				return \$response;
-			}
-		}
-
-		if ( class_exists( '\WpOrg\Requests\Transport\Curl' ) ) {
-			return ( new \WpOrg\Requests\Transport\Curl() )->request( \$url, \$headers, \$data, \$options );
-		}
-
-		return ( new \Requests_Transport_cURL() )->request( \$url, \$headers, \$data, \$options );
-	}
-
-	public function request_multiple( \$requests, \$options ) {
-		throw new Exception( 'Method not implemented: ' . __METHOD__ );
-	}
-
-	public static function test( \$capabilities = array() ) {
-		return true;
-	}
-}
-
-if ( interface_exists( '\WpOrg\Requests\Transport' ) ) {
-	class WP_CLI_Tests_Mock_Requests_Transport implements \WpOrg\Requests\Transport {
-		use WP_CLI_Tests_Mock_Requests_Trait;
-	}
-} else {
-	class WP_CLI_Tests_Mock_Requests_Transport implements \Requests_Transport {
-		use WP_CLI_Tests_Mock_Requests_Trait;
-	}
-}
-
-WP_CLI::add_hook(
-	'http_request_options',
-	static function( \$options ) {
-		\$options['transport'] = new WP_CLI_Tests_Mock_Requests_Transport();
-		return \$options;
-	}
-);
-
-WP_CLI::add_wp_hook(
-	'pre_http_request',
-	static function( \$pre, \$parsed_args, \$url ) {
-		\$mocked_requests = $mocked_requests;
-
-		foreach ( \$mocked_requests as \$pattern => \$response ) {
-			\$pattern = '/' . preg_quote( \$pattern, '/' ) . '/';
-			if ( 1 === preg_match( \$pattern, \$url ) ) {
-				\$pos = strpos( \$response, "\n\n");
-				if ( false !== \$pos ) {
-					\$response = substr( \$response, 0, \$pos ) . "\r\n\r\n" . substr( \$response, \$pos + 2 );
-				}
-
-				if ( class_exists( '\WpOrg\Requests\Requests' ) ) {
-					WpOrg\Requests\Requests::parse_multiple(
-						\$response,
-						array(
-							'url'     => \$url,
-							'headers' => array(),
-							'data'    => array(),
-							'options' => array_merge(
-								WpOrg\Requests\Requests::OPTION_DEFAULTS,
-								array(
-									'hooks' => new WpOrg\Requests\Hooks(),
-								)
-							),
-						)
-					);
-				} else {
-					\Requests::parse_multiple(
-						\$response,
-						array(
-							'url'     => \$url,
-							'headers' => array(),
-							'data'    => array(),
-							'options' => array(
-								'blocking'         => true,
-								'filename'         => false,
-								'follow_redirects' => true,
-								'redirected'       => 0,
-								'redirects'        => 10,
-								'hooks'            => new Requests_Hooks(),
-							),
-						)
-					);
-				}
-
-				if ( ! empty( \$parsed_args['filename'] ) ) {
-					file_put_contents( \$parsed_args['filename'], \$response->body );
-				}
-
-				return array(
-					'headers'  => \$response->headers->getAll(),
-					'body'     => \$response->body,
-					'response' => array(
-						'code'    => \$response->status_code,
-						'message' => get_status_header_desc( \$response->status_code ),
-					),
-					'cookies'  => array(),
-					'filename' => '',
-				);
-			}
-		}
-
-		return \$pre;
-	},
-	10,
-	3
-);
-FILE;
-
 		file_put_contents(
-			$mock_file,
-			$mock_file_contents
+			$data_file,
+			'<?php' . PHP_EOL . 'return ' . var_export( $this->mocked_requests, true /* return */ ) . ';' . PHP_EOL
 		);
+
+		copy( __DIR__ . '/templates/mock-requests.php', $mock_file );
 	}
 
 	/**
diff --git a/src/Context/templates/mock-requests.php b/src/Context/templates/mock-requests.php
new file mode 100644
index 00000000..db3afe07
--- /dev/null
+++ b/src/Context/templates/mock-requests.php
@@ -0,0 +1,135 @@
+<?php
+/**
+ * HTTP request mocking supporting both Requests v1 and v2.
+ *
+ * This file is copied verbatim into the test run directory by
+ * `WP_CLI\Tests\Context\GivenStepDefinitions::given_a_request_to_a_url_respond_with_file()`.
+ * The mocked responses themselves are generated next to it as `mock-requests-data.php`.
+ */
+
+trait WP_CLI_Tests_Mock_Requests_Trait {
+	public function request( $url, $headers = array(), $data = array(), $options = array() ) {
+		$mocked_requests = require __DIR__ . '/mock-requests-data.php';
+
+		foreach ( $mocked_requests as $pattern => $response ) {
+			$pattern = '/' . preg_quote( $pattern, '/' ) . '/';
+			if ( 1 === preg_match( $pattern, $url ) ) {
+				$pos = strpos( $response, "\n\n" );
+				if ( false !== $pos ) {
+					$response = substr( $response, 0, $pos ) . "\r\n\r\n" . substr( $response, $pos + 2 );
+				}
+				if ( ! empty( $options['filename'] ) ) {
+					$body     = '';
+					$body_pos = strpos( $response, "\r\n\r\n" );
+					if ( false !== $body_pos ) {
+						$body = substr( $response, $body_pos + 4 );
+					}
+					file_put_contents( $options['filename'], $body );
+				}
+				return $response;
+			}
+		}
+
+		if ( class_exists( '\WpOrg\Requests\Transport\Curl' ) ) {
+			return ( new \WpOrg\Requests\Transport\Curl() )->request( $url, $headers, $data, $options );
+		}
+
+		return ( new \Requests_Transport_cURL() )->request( $url, $headers, $data, $options );
+	}
+
+	public function request_multiple( $requests, $options ) {
+		throw new Exception( 'Method not implemented: ' . __METHOD__ );
+	}
+
+	public static function test( $capabilities = array() ) {
+		return true;
+	}
+}
+
+if ( interface_exists( '\WpOrg\Requests\Transport' ) ) {
+	class WP_CLI_Tests_Mock_Requests_Transport implements \WpOrg\Requests\Transport {
+		use WP_CLI_Tests_Mock_Requests_Trait;
+	}
+} else {
+	class WP_CLI_Tests_Mock_Requests_Transport implements \Requests_Transport {
+		use WP_CLI_Tests_Mock_Requests_Trait;
+	}
+}
+
+WP_CLI::add_hook(
+	'http_request_options',
+	static function ( $options ) {
+		$options['transport'] = new WP_CLI_Tests_Mock_Requests_Transport();
+		return $options;
+	}
+);
+
+WP_CLI::add_wp_hook(
+	'pre_http_request',
+	static function ( $pre, $parsed_args, $url ) {
+		$mocked_requests = require __DIR__ . '/mock-requests-data.php';
+
+		foreach ( $mocked_requests as $pattern => $response ) {
+			$pattern = '/' . preg_quote( $pattern, '/' ) . '/';
+			if ( 1 === preg_match( $pattern, $url ) ) {
+				$pos = strpos( $response, "\n\n" );
+				if ( false !== $pos ) {
+					$response = substr( $response, 0, $pos ) . "\r\n\r\n" . substr( $response, $pos + 2 );
+				}
+
+				if ( class_exists( '\WpOrg\Requests\Requests' ) ) {
+					WpOrg\Requests\Requests::parse_multiple(
+						$response,
+						array(
+							'url'     => $url,
+							'headers' => array(),
+							'data'    => array(),
+							'options' => array_merge(
+								WpOrg\Requests\Requests::OPTION_DEFAULTS,
+								array(
+									'hooks' => new WpOrg\Requests\Hooks(),
+								)
+							),
+						)
+					);
+				} else {
+					\Requests::parse_multiple(
+						$response,
+						array(
+							'url'     => $url,
+							'headers' => array(),
+							'data'    => array(),
+							'options' => array(
+								'blocking'         => true,
+								'filename'         => false,
+								'follow_redirects' => true,
+								'redirected'       => 0,
+								'redirects'        => 10,
+								'hooks'            => new Requests_Hooks(),
+							),
+						)
+					);
+				}
+
+				if ( ! empty( $parsed_args['filename'] ) ) {
+					file_put_contents( $parsed_args['filename'], $response->body );
+				}
+
+				return array(
+					'headers'  => $response->headers->getAll(),
+					'body'     => $response->body,
+					'response' => array(
+						'code'    => $response->status_code,
+						'message' => get_status_header_desc( $response->status_code ),
+					),
+					'cookies'  => array(),
+					'filename' => '',
+				);
+			}
+		}
+
+		return $pre;
+	},
+	10,
+	3
+);