diff --git a/test/function/allows-external-modules-from-nested-module/_config.js b/test/function/allows-external-modules-from-nested-module/_config.js
index 918a11a..d0c980e 100644
--- a/test/function/allows-external-modules-from-nested-module/_config.js
+++ b/test/function/allows-external-modules-from-nested-module/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'imports external modules from nested internal modules'
+	description: 'imports external modules from nested internal modules',
+	options: {
+		external: [ 'path' ]
+	}
 };
diff --git a/test/function/custom-external-resolver-async/_config.js b/test/function/custom-external-resolver-async/_config.js
new file mode 100644
index 0000000..34faf37
--- /dev/null
+++ b/test/function/custom-external-resolver-async/_config.js
@@ -0,0 +1,15 @@
+var path = require( 'path' );
+var assert = require( 'assert' );
+var Promise = require( 'sander' ).Promise;
+
+module.exports = {
+	description: 'uses a custom external path resolver (asynchronous)',
+	options: {
+		resolveExternal: function ( id, importer, options ) {
+			return Promise.resolve( path.resolve( __dirname, 'js_modules', id + '.js' ) );
+		}
+	},
+	exports: function ( exports ) {
+		assert.ok( exports.success );
+	}
+};
diff --git a/test/function/custom-external-resolver-async/js_modules/external.js b/test/function/custom-external-resolver-async/js_modules/external.js
new file mode 100644
index 0000000..c1547ab
--- /dev/null
+++ b/test/function/custom-external-resolver-async/js_modules/external.js
@@ -0,0 +1 @@
+export default { isExternal: true };
diff --git a/test/function/custom-external-resolver-async/main.js b/test/function/custom-external-resolver-async/main.js
new file mode 100644
index 0000000..32214bd
--- /dev/null
+++ b/test/function/custom-external-resolver-async/main.js
@@ -0,0 +1,3 @@
+import external from 'external';
+
+export default { success: external.isExternal };
diff --git a/test/function/custom-external-resolver-sync/_config.js b/test/function/custom-external-resolver-sync/_config.js
new file mode 100644
index 0000000..2cf6de7
--- /dev/null
+++ b/test/function/custom-external-resolver-sync/_config.js
@@ -0,0 +1,14 @@
+var path = require( 'path' );
+var assert = require( 'assert' );
+
+module.exports = {
+	description: 'uses a custom external path resolver (synchronous)',
+	options: {
+		resolveExternal: function ( id, importer, options ) {
+			return path.resolve( __dirname, 'js_modules', id + '.js' );
+		}
+	},
+	exports: function ( exports ) {
+		assert.ok( exports.success );
+	}
+};
diff --git a/test/function/custom-external-resolver-sync/js_modules/external.js b/test/function/custom-external-resolver-sync/js_modules/external.js
new file mode 100644
index 0000000..c1547ab
--- /dev/null
+++ b/test/function/custom-external-resolver-sync/js_modules/external.js
@@ -0,0 +1 @@
+export default { isExternal: true };
diff --git a/test/function/custom-external-resolver-sync/main.js b/test/function/custom-external-resolver-sync/main.js
new file mode 100644
index 0000000..32214bd
--- /dev/null
+++ b/test/function/custom-external-resolver-sync/main.js
@@ -0,0 +1,3 @@
+import external from 'external';
+
+export default { success: external.isExternal };
diff --git a/test/function/import-default-from-external/_config.js b/test/function/import-default-from-external/_config.js
index d2d3885..98651b7 100644
--- a/test/function/import-default-from-external/_config.js
+++ b/test/function/import-default-from-external/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'imports default from external module'
-};
\ No newline at end of file
+	description: 'imports default from external module',
+	options: {
+		external: [ 'path' ]
+	}
+};
diff --git a/test/function/import-named-from-external/_config.js b/test/function/import-named-from-external/_config.js
index 243412e..cab932b 100644
--- a/test/function/import-named-from-external/_config.js
+++ b/test/function/import-named-from-external/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'imports names from an external module'
-};
\ No newline at end of file
+	description: 'imports names from an external module',
+	options: {
+		external: [ 'path' ]
+	}
+};
diff --git a/test/function/import-namespace-from-external-module-renamed/_config.js b/test/function/import-namespace-from-external-module-renamed/_config.js
index 86394b3..4cb00de 100644
--- a/test/function/import-namespace-from-external-module-renamed/_config.js
+++ b/test/function/import-namespace-from-external-module-renamed/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'imports a namespace from an external module and renames it'
+	description: 'imports a namespace from an external module and renames it',
+	options: {
+		external: [ 'path' ]
+	}
 };
diff --git a/test/function/import-namespace-from-external-module/_config.js b/test/function/import-namespace-from-external-module/_config.js
index f107139..3704e5c 100644
--- a/test/function/import-namespace-from-external-module/_config.js
+++ b/test/function/import-namespace-from-external-module/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'imports a namespace from an external module'
-};
\ No newline at end of file
+	description: 'imports a namespace from an external module',
+	options: {
+		external: [ 'path' ]
+	}
+};
diff --git a/test/function/imports-are-deconflicted-b/_config.js b/test/function/imports-are-deconflicted-b/_config.js
index a7c1041..eceba93 100644
--- a/test/function/imports-are-deconflicted-b/_config.js
+++ b/test/function/imports-are-deconflicted-b/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'deconflicts imports (redux)'
+	description: 'deconflicts imports (redux)',
+	options: {
+		external: [ 'path' ]
+	}
 };
diff --git a/test/function/imports-are-deconflicted/_config.js b/test/function/imports-are-deconflicted/_config.js
index 49dbfd8..345f6b8 100644
--- a/test/function/imports-are-deconflicted/_config.js
+++ b/test/function/imports-are-deconflicted/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'deconflicts imports'
+	description: 'deconflicts imports',
+	options: {
+		external: [ 'path' ]
+	}
 };
diff --git a/test/function/legal-import-modification/_config.js b/test/function/legal-import-modification/_config.js
new file mode 100644
index 0000000..3792857
--- /dev/null
+++ b/test/function/legal-import-modification/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'assigning to properties of imported bindings is permitted'
+};
diff --git a/test/function/legal-import-modification/foo.js b/test/function/legal-import-modification/foo.js
new file mode 100644
index 0000000..ff8b4c5
--- /dev/null
+++ b/test/function/legal-import-modification/foo.js
@@ -0,0 +1 @@
+export default {};
diff --git a/test/function/legal-import-modification/main.js b/test/function/legal-import-modification/main.js
new file mode 100644
index 0000000..455d804
--- /dev/null
+++ b/test/function/legal-import-modification/main.js
@@ -0,0 +1,5 @@
+import foo from './foo';
+
+foo.modified = true;
+
+export default foo;
diff --git a/test/function/shadowed-external-export/_config.js b/test/function/shadowed-external-export/_config.js
index b39af37..2a744dc 100644
--- a/test/function/shadowed-external-export/_config.js
+++ b/test/function/shadowed-external-export/_config.js
@@ -1,3 +1,6 @@
 module.exports = {
-	description: 'external modules are not shadowed'
+	description: 'external modules are not shadowed',
+	options: {
+		external: [ 'path' ]
+	}
 };
diff --git a/test/function/transformer-multiple/_config.js b/test/function/transformer-multiple/_config.js
new file mode 100644
index 0000000..34ddbf7
--- /dev/null
+++ b/test/function/transformer-multiple/_config.js
@@ -0,0 +1,21 @@
+var assert = require( 'assert' );
+
+module.exports = {
+	description: 'accepts multiple transformer functions',
+	options: {
+		transform: [
+			function ( code, path ) {
+				return code.replace( /MAGIC_NUMBER/g, 3 );
+			},
+
+			function ( code, path ) {
+				return code.replace( /\d+/g, function ( match ) {
+					return 2 * +match;
+				});
+			}
+		]
+	},
+	exports: function ( exports ) {
+		assert.equal( exports.magicNumber, 6 );
+	}
+}
diff --git a/test/function/transformer-multiple/foo.js b/test/function/transformer-multiple/foo.js
new file mode 100644
index 0000000..119481e
--- /dev/null
+++ b/test/function/transformer-multiple/foo.js
@@ -0,0 +1 @@
+export default MAGIC_NUMBER;
diff --git a/test/function/transformer-multiple/main.js b/test/function/transformer-multiple/main.js
new file mode 100644
index 0000000..0fb821d
--- /dev/null
+++ b/test/function/transformer-multiple/main.js
@@ -0,0 +1,3 @@
+import foo from './foo';
+
+export var magicNumber = foo;
diff --git a/test/function/transformer-single/_config.js b/test/function/transformer-single/_config.js
new file mode 100644
index 0000000..4cf7a76
--- /dev/null
+++ b/test/function/transformer-single/_config.js
@@ -0,0 +1,13 @@
+var assert = require( 'assert' );
+
+module.exports = {
+	description: 'accepts a single transformer function',
+	options: {
+		transform: function ( code, path ) {
+			return code.replace( /MAGIC_NUMBER/g, 3 );
+		}
+	},
+	exports: function ( exports ) {
+		assert.equal( exports.magicNumber, 3 );
+	}
+}
diff --git a/test/function/transformer-single/foo.js b/test/function/transformer-single/foo.js
new file mode 100644
index 0000000..119481e
--- /dev/null
+++ b/test/function/transformer-single/foo.js
@@ -0,0 +1 @@
+export default MAGIC_NUMBER;
diff --git a/test/function/transformer-single/main.js b/test/function/transformer-single/main.js
new file mode 100644
index 0000000..0fb821d
--- /dev/null
+++ b/test/function/transformer-single/main.js
@@ -0,0 +1,3 @@
+import foo from './foo';
+
+export var magicNumber = foo;