diff --git a/inc/manifest.php b/inc/manifest.php
index d42bbf1..b60d7b8 100644
--- a/inc/manifest.php
+++ b/inc/manifest.php
@@ -106,10 +106,10 @@ function get_version( string $asset_uri, string $manifest_path ) : ?string {
 		if ( $manifest_hash ) {
 			$manifest_hashes[ $manifest_path ] = $manifest_hash;
 			return $manifest_hashes[ $manifest_path ];
+		} else {
+			// Set "null" to prevent trying to re-hash after hashing has failed once.
+			$manifest_hashes[ $manifest_path ] = null;
 		}
-	} else {
-		// Set "null" to prevent subsequent file_exists checks during this request.
-		$manifest_hashes[ $manifest_path ] = null;
 	}
 
 	// Finally, use the Altis deployment revision when available. This is a
diff --git a/inc/namespace.php b/inc/namespace.php
index ff2739f..fddff40 100644
--- a/inc/namespace.php
+++ b/inc/namespace.php
@@ -185,7 +185,7 @@ function( $script_key ) use ( $target_bundle ) {
 	$css_bundle = $build_path . preg_replace( '/\.js$/', '.css', $target_bundle );
 
 	// Production mode. Manually register script bundles.
-	if ( file_exists( $js_bundle ) ) {
+	if ( is_readable( $js_bundle ) ) {
 		wp_register_script(
 			$options['handle'],
 			Paths\get_file_uri( $js_bundle ),
@@ -196,7 +196,7 @@ function( $script_key ) use ( $target_bundle ) {
 		$registered['scripts'][] = $options['handle'];
 	}
 
-	if ( file_exists( $css_bundle ) ) {
+	if ( is_readable( $css_bundle ) ) {
 		wp_register_style(
 			$options['handle'],
 			Paths\get_file_uri( $css_bundle ),
@@ -310,11 +310,12 @@ function _register_or_update_script( string $handle, string $asset_uri, array $d
  * @param string $manifest_path File system path for an asset manifest JSON file.
  * @param string $target_asset  Asset to retrieve within the specified manifest.
  * @param array  $options {
- *     @type string $handle       Handle to use when enqueuing the asset. Required.
+ *     @type string $handle       Handle to use when enqueuing the asset. Optional.
  *     @type array  $dependencies Script or Style dependencies. Optional.
  * }
+ * @return array Array detailing which script and/or style handles got registered.
  */
-function register_asset( string $manifest_path, string $target_asset, array $options = [] ) : void {
+function register_asset( string $manifest_path, string $target_asset, array $options = [] ) : array {
 	$defaults = [
 		'dependencies' => [],
 	];
@@ -338,82 +339,88 @@ function register_asset( string $manifest_path, string $target_asset, array $opt
 
 	// If asset is not present in manifest, attempt to resolve the $target_asset
 	// relative to the folder containing the manifest file.
-	if ( empty( $asset_uri ) && file_exists( $manifest_folder . $target_asset ) ) {
-		// TODO: Consider checking file_exists( $manifest_folder . $target_asset )
+	if ( empty( $asset_uri ) ) {
+		// TODO: Consider checking is_readable( $manifest_folder . $target_asset )
 		// and warning (in console or error log) if it is not present on disk.
 		$asset_uri = $target_asset;
 	}
 
-	// Use the asset URI as the asset handle if no handle was provided.
-	if ( empty( $options['handle'] ) ) {
-		$options['handle'] = $asset_uri;
-	}
-
 	// Reconcile static asset build paths relative to the manifest's directory.
 	if ( strpos( $asset_uri, '//' ) === false ) {
 		$asset_uri = Paths\get_file_uri( $manifest_folder . $asset_uri );
 	}
 
+	// Use the requested asset as the asset handle if no handle was provided.
+	$asset_handle = $options['handle'] ?? $target_asset;
 	$asset_version = Manifest\get_version( $asset_uri, $manifest_path );
 
+	// Track registered handles so we can enqueue the correct assets later.
+	$handles = [];
+
 	if ( is_css( $asset_uri ) ) {
 		// Register a normal CSS bundle.
 		wp_register_style(
-			$options['handle'],
+			$asset_handle,
 			$asset_uri,
 			$options['dependencies'],
 			$asset_version
 		);
+		$handles['style'] = $asset_handle;
 	} elseif ( $is_js_style_fallback ) {
 		// We're registering a JS bundle when we originally asked for a CSS bundle.
 		// Register the JS, but if any dependencies were passed in, also register a
 		// dummy style bundle so that those style dependencies still get loaded.
 		Admin\maybe_setup_ssl_cert_error_handling( $asset_uri );
 		_register_or_update_script(
-			$options['handle'],
+			$asset_handle,
 			$asset_uri,
 			[],
 			$asset_version,
 			true
 		);
+		$handles['script'] = $asset_handle;
 		if ( ! empty( $options['dependencies'] ) ) {
 			wp_register_style(
-				$options['handle'],
+				$asset_handle,
 				false,
 				$options['dependencies'],
 				$asset_version
 			);
+			$handles['style'] = $asset_handle;
 		}
 	} else {
 		// Register a normal JS bundle.
 		Admin\maybe_setup_ssl_cert_error_handling( $asset_uri );
 		_register_or_update_script(
-			$options['handle'],
+			$asset_handle,
 			$asset_uri,
 			$options['dependencies'],
 			$asset_version,
 			true
 		);
+		$handles['script'] = $asset_handle;
 	}
+
+	return $handles;
 }
 
 /**
- * Attempt to register and then enqueue a particular script bundle from a manifest.
+ * Register and immediately enqueue a particular asset within a manifest.
  *
  * @param string $manifest_path File system path for an asset manifest JSON file.
  * @param string $target_asset  Asset to retrieve within the specified manifest.
  * @param array  $options {
- *     @type string $handle       Handle to use when enqueuing the asset. Required.
+ *     @type string $handle       Handle to use when enqueuing the asset. Optional.
  *     @type array  $dependencies Script or Style dependencies. Optional.
  * }
  */
 function enqueue_asset( string $manifest_path, string $target_asset, array $options = [] ) : void {
-	register_asset( $manifest_path, $target_asset, $options );
+	$registered_handles = register_asset( $manifest_path, $target_asset, $options );
 
-	// $target_asset will share a filename extension with the enqueued asset.
-	if ( is_css( $target_asset ) ) {
-		wp_enqueue_style( $options['handle'] );
-	} else {
-		wp_enqueue_script( $options['handle'] );
+	if ( isset( $registered_handles['script'] ) ) {
+		wp_enqueue_script( $registered_handles['script'] );
+	}
+	if ( isset( $registered_handles['style'] ) ) {
+		wp_enqueue_style( $registered_handles['style'] );
 	}
 }
diff --git a/tests/inc/class-test-asset-loader.php b/tests/inc/class-test-asset-loader.php
index 923c31a..af0cda4 100644
--- a/tests/inc/class-test-asset-loader.php
+++ b/tests/inc/class-test-asset-loader.php
@@ -111,102 +111,246 @@ public function provide_is_css_cases() {
 	}
 
 	/**
-	 * Test register_asset() behavior with production JS assets.
+	 * Test register_asset() behavior for script assets.
+	 *
+	 * @dataProvider provide_script_asset_cases
 	 */
-	public function test_register_prod_script() : void {
-		Asset_Loader\enqueue_asset( $this->prod_manifest, 'editor.js', [
-			'handle' => 'custom-handle',
-			'dependencies' => [ 'wp-data' ],
-		] );
+	public function test_register_script( string $manifest, string $resource, array $options, array $expected ) : void {
+		Asset_Loader\register_asset( $this->{$manifest}, $resource, $options );
 
-		$this->assertEquals(
-			[
-				'handle'   => 'custom-handle',
-				'src'      => 'https://my.theme/uri/fixtures/editor.03bfa96fd1c694ca18b3.js',
-				'deps'     => [ 'wp-data' ],
-				'ver'      => null,
+		$this->assertEquals( $expected, $this->scripts->get_registered( $expected['handle'] ) );
+	}
+
+	/**
+	 * Test enqueue_asset() behavior for script assets.
+	 *
+	 * @dataProvider provide_script_asset_cases
+	 */
+	public function test_enqueue_script( string $manifest, string $resource, array $options, array $expected ) : void {
+		Asset_Loader\enqueue_asset( $this->{$manifest}, $resource, $options );
+
+		$this->assertEquals( $expected, $this->scripts->get_registered( $expected['handle'] ) );
+		$this->assertEmpty( $this->styles->registered );
+
+		$this->assertEquals( [ $expected['handle'] ], $this->scripts->get_enqueued() );
+	}
+
+	/**
+	 * Script test cases for register_asset and enqueue_asset.
+	 */
+	public function provide_script_asset_cases() : array {
+		return [
+			'production script' => [
+				'prod_manifest',
+				'editor.js',
+				[
+					'handle'       => 'custom-handle',
+					'dependencies' => [ 'wp-data' ],
+				],
+				[
+					'handle' => 'custom-handle',
+					'src'    => 'https://my.theme/uri/fixtures/editor.03bfa96fd1c694ca18b3.js',
+					'deps'   => [ 'wp-data' ],
+					'ver'    => null,
+				],
 			],
-			$this->scripts->get_registered( 'custom-handle' )
-		);
+			'development script' => [
+				'dev_manifest',
+				'editor.js',
+				[
+					'handle'       => 'editor-bundle',
+					'dependencies' => [ 'wp-data', 'wp-element' ],
+				],
+				[
+					'handle' => 'editor-bundle',
+					'src'    => 'https://localhost:9090/build/editor.js',
+					'deps'   => [ 'wp-data', 'wp-element' ],
+					'ver'    => '499bb147f8e7234d957a47ac983e19e7',
+				],
+			],
+		];
+	}
+
+	/**
+	 * Test register_asset() behavior for style assets.
+	 *
+	 * @dataProvider provide_style_asset_cases
+	 */
+	public function test_register_style( string $manifest, string $resource, array $options, array $expected ) : void {
+		Asset_Loader\register_asset( $this->{$manifest}, $resource, $options );
+
+		$this->assertEquals( $expected, $this->styles->get_registered( $expected['handle'] ) );
+	}
+
+	/**
+	 * Test enqueue_asset() behavior for style assets.
+	 *
+	 * @dataProvider provide_style_asset_cases
+	 */
+	public function test_enqueue_style( string $manifest, string $resource, array $options, array $expected ) : void {
+		Asset_Loader\enqueue_asset( $this->{$manifest}, $resource, $options );
+
+		$this->assertEquals( $expected, $this->styles->get_registered( $expected['handle'] ) );
+		$this->assertEmpty( $this->scripts->registered );
+
+		$this->assertEquals( [ $expected['handle'] ], $this->styles->get_enqueued() );
 	}
 
 	/**
-	 * Test enqueue_asset() behavior with production JS assets.
+	 * Stylesheet test cases for register_asset and enqueue_asset.
 	 */
-	public function test_enqueue_prod_script() : void {
-		Asset_Loader\enqueue_asset( $this->prod_manifest, 'editor.js', [
-			'handle' => 'custom-handle',
-			'dependencies' => [ 'wp-data' ],
-		] );
+	public function provide_style_asset_cases() : array {
+		return [
+			'production stylesheet' => [
+				'prod_manifest',
+				'frontend-styles.css',
+				[
+					'handle'       => 'frontend-styles',
+					'dependencies' => [ 'dependency-style' ],
+				],
+				[
+					'handle' => 'frontend-styles',
+					'src'    => 'https://my.theme/uri/fixtures/frontend-styles.96a500e3dd1eb671f25e.css',
+					'deps'   => [ 'dependency-style' ],
+					'ver'    => null,
+				],
+			],
+			'production stylesheet with no explicit handle' => [
+				'prod_manifest',
+				'frontend-styles.css',
+				[
+					'dependencies' => [ 'dependency-style' ],
+				],
+				[
+					'handle' => 'frontend-styles.css',
+					'src'    => 'https://my.theme/uri/fixtures/frontend-styles.96a500e3dd1eb671f25e.css',
+					'deps'   => [ 'dependency-style' ],
+					'ver'    => null,
+				],
+			],
+			'production stylesheet not in manifest' => [
+				'prod_manifest',
+				'theme.css',
+				[],
+				[
+					'handle' => 'theme.css',
+					'src'    => 'https://my.theme/uri/fixtures/theme.css',
+					'deps'   => [],
+					'ver'    => '2a9dea09d6ed09f7c4ce052b82cc4999',
+				],
+			],
+		];
+	}
 
+	public function test_register_dev_stylesheet() : void {
+		Asset_Loader\register_asset(
+			$this->dev_manifest,
+			'frontend-styles.css',
+			[
+				'handle' => 'frontend-styles',
+			]
+		);
 		$this->assertEquals(
 			[
-				'handle'   => 'custom-handle',
-				'src'      => 'https://my.theme/uri/fixtures/editor.03bfa96fd1c694ca18b3.js',
-				'deps'     => [ 'wp-data' ],
-				'ver'      => null,
+				'handle' => 'frontend-styles',
+				'src'    => 'https://localhost:9090/build/frontend-styles.js',
+				'deps'   => [],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
 			],
-			$this->scripts->get_registered( 'custom-handle' )
+			$this->scripts->get_registered( 'frontend-styles' )
 		);
+		$this->assertEquals( [], $this->styles->registered );
+	}
 
-		$this->assertEquals( [ 'custom-handle' ], $this->scripts->get_enqueued() );
+	public function test_enqueue_dev_stylesheet() : void {
+		Asset_Loader\enqueue_asset(
+			$this->dev_manifest,
+			'frontend-styles.css',
+			[
+				'handle' => 'frontend-styles',
+			]
+		);
+		$this->assertEquals(
+			[
+				'handle' => 'frontend-styles',
+				'src'    => 'https://localhost:9090/build/frontend-styles.js',
+				'deps'   => [],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
+			],
+			$this->scripts->get_registered( 'frontend-styles' )
+		);
+		$this->assertEquals( [], $this->styles->registered );
+
+		$this->assertEquals( [ 'frontend-styles' ], $this->scripts->get_enqueued() );
 	}
 
-	public function test_register_css_asset_production() : void {
+	public function test_register_dev_stylesheet_with_dependencies() : void {
 		Asset_Loader\register_asset(
-			$this->prod_manifest,
+			$this->dev_manifest,
 			'frontend-styles.css',
 			[
-				'handle' => 'frontend-styles',
+				'handle'       => 'frontend-styles',
 				'dependencies' => [ 'dependency-style' ],
 			]
 		);
 		$this->assertEquals(
 			[
 				'handle' => 'frontend-styles',
-				'src' => 'https://my.theme/uri/fixtures/frontend-styles.96a500e3dd1eb671f25e.css',
-				'deps' => [ 'dependency-style' ],
-				'ver' => null,
+				'src'    => 'https://localhost:9090/build/frontend-styles.js',
+				'deps'   => [],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
+			],
+			$this->scripts->get_registered( 'frontend-styles' )
+		);
+		$this->assertEquals(
+			[
+				'handle' => 'frontend-styles',
+				'src'    => false,
+				'deps'   => [ 'dependency-style' ],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
 			],
 			$this->styles->get_registered( 'frontend-styles' )
 		);
 	}
 
-	public function test_register_css_asset_dev() : void {
-		Asset_Loader\register_asset(
+	public function test_enqueue_dev_stylesheet_with_dependencies() : void {
+		Asset_Loader\enqueue_asset(
 			$this->dev_manifest,
 			'frontend-styles.css',
 			[
-				'handle' => 'frontend-styles',
+				'handle'       => 'frontend-styles',
 				'dependencies' => [ 'dependency-style' ],
 			]
 		);
 		$this->assertEquals(
 			[
 				'handle' => 'frontend-styles',
-				'src' => 'https://localhost:9090/build/frontend-styles.js',
-				'deps' => [],
-				'ver' => '499bb147f8e7234d957a47ac983e19e7',
+				'src'    => 'https://localhost:9090/build/frontend-styles.js',
+				'deps'   => [],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
 			],
 			$this->scripts->get_registered( 'frontend-styles' )
 		);
 		$this->assertEquals(
 			[
 				'handle' => 'frontend-styles',
-				'src' => false,
-				'deps' => [ 'dependency-style' ],
-				'ver' => '499bb147f8e7234d957a47ac983e19e7',
+				'src'    => false,
+				'deps'   => [ 'dependency-style' ],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
 			],
 			$this->styles->get_registered( 'frontend-styles' )
 		);
+
+		$this->assertEquals( [ 'frontend-styles' ], $this->scripts->get_enqueued() );
+		$this->assertEquals( [ 'frontend-styles' ], $this->styles->get_enqueued() );
 	}
 
-	public function test_register_css_asset_then_corresponding_js_asset_dev() : void {
+	public function test_register_dev_stylesheet_then_corresponding_dev_script() : void {
 		Asset_Loader\register_asset(
 			$this->dev_manifest,
 			'editor.css',
 			[
-				'handle' => 'editor',
+				'handle'       => 'editor',
 				'dependencies' => [ 'style-dependency' ],
 			]
 		);
@@ -214,35 +358,67 @@ public function test_register_css_asset_then_corresponding_js_asset_dev() : void
 			$this->dev_manifest,
 			'editor.js',
 			[
-				'handle' => 'editor',
+				'handle'       => 'editor',
 				'dependencies' => [ 'script-dependency' ],
 			]
 		);
 		$this->assertEquals(
 			[
 				'handle' => 'editor',
-				'src' => 'https://localhost:9090/build/editor.js',
-				'deps' => [ 'script-dependency' ],
-				'ver' => '499bb147f8e7234d957a47ac983e19e7',
+				'src'    => 'https://localhost:9090/build/editor.js',
+				'deps'   => [ 'script-dependency' ],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
 			],
 			$this->scripts->get_registered( 'editor' )
 		);
 		$this->assertEquals(
 			[
 				'handle' => 'editor',
-				'src' => false,
-				'deps' => [ 'style-dependency' ],
-				'ver' => '499bb147f8e7234d957a47ac983e19e7',
+				'src'    => false,
+				'deps'   => [ 'style-dependency' ],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
 			],
 			$this->styles->get_registered( 'editor' )
 		);
 	}
 
-	/*
-	- Load dev JS file (simple case)
-	- Load prod JS file (simple case)
-	- Load production CSS file (simple case)
-	- enqueue CSS that falls back to JS
-	- enqueue CSS that falls back to JS *and() JS and ensure both their dependencies get handled
-	*/
+	public function test_enqueue_dev_stylesheet_then_corresponding_dev_script() : void {
+		Asset_Loader\enqueue_asset(
+			$this->dev_manifest,
+			'editor.css',
+			[
+				'handle'       => 'editor',
+				'dependencies' => [ 'style-dependency' ],
+			]
+		);
+		Asset_Loader\enqueue_asset(
+			$this->dev_manifest,
+			'editor.js',
+			[
+				'handle'       => 'editor',
+				'dependencies' => [ 'script-dependency' ],
+			]
+		);
+		$this->assertEquals(
+			[
+				'handle' => 'editor',
+				'src'    => 'https://localhost:9090/build/editor.js',
+				'deps'   => [ 'script-dependency' ],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
+			],
+			$this->scripts->get_registered( 'editor' )
+		);
+		$this->assertEquals(
+			[
+				'handle' => 'editor',
+				'src'    => false,
+				'deps'   => [ 'style-dependency' ],
+				'ver'    => '499bb147f8e7234d957a47ac983e19e7',
+			],
+			$this->styles->get_registered( 'editor' )
+		);
+
+		$this->assertEquals( [ 'editor' ], $this->scripts->get_enqueued() );
+		$this->assertEquals( [ 'editor' ], $this->styles->get_enqueued() );
+	}
 }