diff --git a/tests/fixtures/hard-source-confighash-dir/config-hash b/tests/fixtures/hard-source-confighash-dir/config-hash
new file mode 100644
index 00000000..63d8dbd4
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash-dir/config-hash
@@ -0,0 +1 @@
+b
\ No newline at end of file
diff --git a/tests/fixtures/hard-source-confighash-dir/fib/index.js b/tests/fixtures/hard-source-confighash-dir/fib/index.js
new file mode 100644
index 00000000..bf0205d4
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash-dir/fib/index.js
@@ -0,0 +1,3 @@
+module.exports = function(n) {
+  return n + (n > 0 ? n - 2 : 0);
+};
\ No newline at end of file
diff --git a/tests/fixtures/hard-source-confighash-dir/index.js b/tests/fixtures/hard-source-confighash-dir/index.js
new file mode 100644
index 00000000..8acf0395
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash-dir/index.js
@@ -0,0 +1,3 @@
+var fib = require('./fib');
+
+console.log(fib(3));
diff --git a/tests/fixtures/hard-source-confighash-dir/webpack.config.js b/tests/fixtures/hard-source-confighash-dir/webpack.config.js
new file mode 100644
index 00000000..1f08a1e5
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash-dir/webpack.config.js
@@ -0,0 +1,24 @@
+var fs = require('fs');
+
+var HardSourceWebpackPlugin = require('../../..');
+
+module.exports = {
+  context: __dirname,
+  entry: './index.js',
+  output: {
+    path: __dirname + '/tmp',
+    filename: 'main.js',
+  },
+  plugins: [
+    new HardSourceWebpackPlugin({
+      cacheDirectory: 'cache/[confighash]',
+      recordsPath: 'cache/[confighash]/records.json',
+      configHash: function(config) {
+        return fs.readFileSync(__dirname + '/config-hash', 'utf8');
+      },
+      environmentPaths: {
+        root: __dirname + '/../../..',
+      },
+    }),
+  ],
+};
diff --git a/tests/fixtures/hard-source-confighash/config-hash b/tests/fixtures/hard-source-confighash/config-hash
new file mode 100644
index 00000000..63d8dbd4
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash/config-hash
@@ -0,0 +1 @@
+b
\ No newline at end of file
diff --git a/tests/fixtures/hard-source-confighash/fib/index.js b/tests/fixtures/hard-source-confighash/fib/index.js
new file mode 100644
index 00000000..bf0205d4
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash/fib/index.js
@@ -0,0 +1,3 @@
+module.exports = function(n) {
+  return n + (n > 0 ? n - 2 : 0);
+};
\ No newline at end of file
diff --git a/tests/fixtures/hard-source-confighash/index.js b/tests/fixtures/hard-source-confighash/index.js
new file mode 100644
index 00000000..8acf0395
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash/index.js
@@ -0,0 +1,3 @@
+var fib = require('./fib');
+
+console.log(fib(3));
diff --git a/tests/fixtures/hard-source-confighash/webpack.config.js b/tests/fixtures/hard-source-confighash/webpack.config.js
new file mode 100644
index 00000000..44a677c8
--- /dev/null
+++ b/tests/fixtures/hard-source-confighash/webpack.config.js
@@ -0,0 +1,24 @@
+var fs = require('fs');
+
+var HardSourceWebpackPlugin = require('../../..');
+
+module.exports = {
+  context: __dirname,
+  entry: './index.js',
+  output: {
+    path: __dirname + '/tmp',
+    filename: 'main.js',
+  },
+  plugins: [
+    new HardSourceWebpackPlugin({
+      cacheDirectory: 'cache',
+      recordsPath: 'cache/records.json',
+      configHash: function(config) {
+        return fs.readFileSync(__dirname + '/config-hash', 'utf8');
+      },
+      environmentPaths: {
+        root: __dirname + '/../../..',
+      },
+    }),
+  ],
+};
diff --git a/tests/hard-source.js b/tests/hard-source.js
new file mode 100644
index 00000000..a58969d5
--- /dev/null
+++ b/tests/hard-source.js
@@ -0,0 +1,51 @@
+var fs = require('fs');
+
+var expect = require('chai').expect;
+
+var itCompilesChange = require('./util').itCompilesChange;
+
+describe('hard-source features', function() {
+
+  itCompilesChange('hard-source-confighash', {
+    'config-hash': 'a',
+    'fib.js': [
+      'module.exports = function(n) {',
+      '  return n + (n > 0 ? n - 1 : 0);',
+      '};',
+    ].join('\n'),
+    'fib/index.js': null,
+  }, {
+    'config-hash': 'b',
+    'fib.js': null,
+    'fib/index.js': [
+      'module.exports = function(n) {',
+      '  return n + (n > 0 ? n - 2 : 0);',
+      '};',
+    ].join('\n'),
+  }, function(output) {
+    expect(fs.readdirSync(__dirname + '/fixtures/hard-source-confighash/tmp/cache'))
+    .to.have.length(6);
+  });
+
+  itCompilesChange('hard-source-confighash-dir', {
+    'config-hash': 'a',
+    'fib.js': [
+      'module.exports = function(n) {',
+      '  return n + (n > 0 ? n - 1 : 0);',
+      '};',
+    ].join('\n'),
+    'fib/index.js': null,
+  }, {
+    'config-hash': 'b',
+    'fib.js': null,
+    'fib/index.js': [
+      'module.exports = function(n) {',
+      '  return n + (n > 0 ? n - 2 : 0);',
+      '};',
+    ].join('\n'),
+  }, function(output) {
+    expect(fs.readdirSync(__dirname + '/fixtures/hard-source-confighash-dir/tmp/cache'))
+    .to.have.length(2);
+  });
+
+});
diff --git a/tests/util/index.js b/tests/util/index.js
index e1f4555b..ef80f098 100644
--- a/tests/util/index.js
+++ b/tests/util/index.js
@@ -1,5 +1,6 @@
 var fs = require('fs');
 var path = require('path');
+var vm = require('vm');
 
 var expect = require('chai').expect;
 var MemoryFS = require('memory-fs');
@@ -8,9 +9,26 @@ var Promise = require('bluebird');
 var rimraf = require('rimraf');
 var webpack = require('webpack');
 
+function wrapModule(code) {
+  return '(function(exports, require, module, __filename, __dirname) {' +
+    code +
+  '})';
+}
+
+function callModule(fn, filename) {
+  var module = {exports: {}};
+  fn(module.exports, Object.assign(function(modulename) {
+    if (/\W/.test(modulename[0])) {
+      return require(path.join(path.dirname(filename), modulename));
+    }
+    return require(modulename);
+  }, require), module, filename, path.dirname(filename));
+  return module.exports;
+}
+
 exports.compile = function(fixturePath) {
-  var configPath = path.join(__dirname, '..', 'fixtures', fixturePath, 'webpack.config');
-  var compiler = webpack(require(configPath));
+  var configPath = path.join(__dirname, '..', 'fixtures', fixturePath, 'webpack.config.js');
+  var compiler = webpack(callModule(vm.runInThisContext(wrapModule(fs.readFileSync(configPath, 'utf8')), {filename: configPath}), configPath));
   var outputfs = compiler.outputFileSystem = new MemoryFS();
   var readdir = Promise.promisify(outputfs.readdir, {context: outputfs});
   var readFile = Promise.promisify(outputfs.readFile, {context: outputfs});