diff --git a/README.md b/README.md
index 9cdadf4a..71c924ca 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,9 @@ and then:
 
 `cross-env COVERAGE=true ember test`
 
-When running with `parallel` set to true, the final reports can be merged by using `ember coverage-merge`. The final merged output will be stored in the `coverageFolder`.
+Coverage also works when running tests in parallel, eg:
+
+`COVERAGE=true ember exam --split=2 --parallel=true`
 
 ## Configuration
 
@@ -46,8 +48,6 @@ Configuration is optional. It should be put in a file at `config/coverage.js` (`
 
 - `coverageFolder`: Defaults to `coverage`. A folder relative to the root of your project to store coverage results.
 
-- `parallel`: Defaults to `false`. Should be set to true if parallel testing is being used, for example when using [ember-exam](https://github.com/trentmwillis/ember-exam) with the `--parallel` flag. This will generate the coverage reports in directories suffixed with `_<random_string>` to avoid overwriting other threads reports. These reports can be joined by using the `ember coverage-merge` command (potentially as part of the [posttest hook](https://docs.npmjs.com/misc/scripts) in your `package.json`).
-
 #### Example
 ```js
   module.exports = {
diff --git a/index.js b/index.js
index bd99eb08..e70a454d 100644
--- a/index.js
+++ b/index.js
@@ -85,29 +85,35 @@ module.exports = {
     return undefined;
   },
 
-  includedCommands: function() {
-    return {
-      'coverage-merge': require('./lib/coverage-merge')
-    };
-  },
-
   /**
    * If coverage is enabled attach coverage middleware to the express server run by ember-cli
    * @param {Object} startOptions - Express server start options
    */
   serverMiddleware: function(startOptions) {
-    this.testemMiddleware(startOptions.app);
+    if (!this._isCoverageEnabled()) {
+      return;
+    }
+    attachMiddleware.serverMiddleware(startOptions.app, {
+      configPath: this.project.configPath(),
+      root: this.project.root,
+      fileLookup: this.fileLookup
+    });
   },
 
   testemMiddleware: function(app) {
     if (!this._isCoverageEnabled()) {
       return;
     }
-    attachMiddleware(app, {
+    const config = {
       configPath: this.project.configPath(),
       root: this.project.root,
       fileLookup: this.fileLookup
-    });
+    };
+    // if we're running `ember test --server` use the `serverMiddleware`.
+    if (process.argv.includes('--server') || process.argv.includes('-s')) {
+      return this.serverMiddleware({ app }, config);
+    }
+    attachMiddleware.testMiddleware(app, config);
   },
 
   // Custom Methods
diff --git a/lib/attach-middleware.js b/lib/attach-middleware.js
index 6f1dab01..af6c96ff 100644
--- a/lib/attach-middleware.js
+++ b/lib/attach-middleware.js
@@ -1,10 +1,11 @@
 'use strict';
 
-var bodyParser = require('body-parser');
-var istanbul = require('istanbul-api');
-var getConfig = require('./config');
-var path = require('path');
-var crypto = require('crypto');
+const bodyParser = require('body-parser').json({ limit: '50mb' });
+const istanbul = require('istanbul-api');
+const getConfig = require('./config');
+const path = require('path');
+
+const WRITE_COVERAGE = '/write-coverage';
 
 function logError(err, req, res, next) {
   console.error(err.stack);
@@ -16,40 +17,52 @@ function fixFilePaths(coverageData, fileLookup) {
   return coverageData;
 }
 
-module.exports = function(app, options) {
-  app.post('/write-coverage',
-    bodyParser.json({ limit: '50mb' }),
-    function(req, res) {
-      var config = getConfig(options.configPath);
-
-      if (config.parallel) {
-        config.coverageFolder = config.coverageFolder + '_' + crypto.randomBytes(4).toString('hex');
-        if (config.reporters.indexOf('json') === -1) {
-          config.reporters.push('json');
-        }
-      }
-
-      if (config.reporters.indexOf('json-summary') === -1) {
-        config.reporters.push('json-summary');
-      }
-
-      let reporter = istanbul.createReporter();
-      if (config.coverageFolder) {
-        reporter.dir = path.join(options.root, config.coverageFolder);
-      }
-      let map = istanbul.libCoverage.createCoverageMap();
-      let coverage = req.body;
+function writeCoverage(coverage, fileLookup, map) {
+  Object.keys(fileLookup).forEach(filename => {
+    let fileCoverage = coverage[filename] || istanbul.libCoverage.createFileCoverage(filename).data;
+    map.addFileCoverage(fixFilePaths(fileCoverage, fileLookup));
+  });
+}
 
-      Object.keys(options.fileLookup).forEach(filename => {
-        let fileCoverage = coverage[filename] || istanbul.libCoverage.createFileCoverage(filename).data;
-        map.addFileCoverage(fixFilePaths(fileCoverage, options.fileLookup));
-      });
+function reportCoverage(map, root, configPath) {
+  let config = getConfig(configPath);
+  let reporter = istanbul.createReporter();
+  if (config.coverageFolder) {
+    reporter.dir = path.join(root, config.coverageFolder);
+  }
+  reporter.addAll(config.reporters);
+  reporter.write(map);
+}
 
-      reporter.addAll(config.reporters);
-      reporter.write(map);
+function coverageHandler(map, options, req, res) {
+  writeCoverage(req.body, options.fileLookup, map);
+  reportCoverage(map, options.root, options.configPath);
+  res.send(map.getCoverageSummary());
+}
 
-      const results = map.getCoverageSummary();
-      res.send(results);
+// Used when app is in dev mode (`ember serve`).
+// Creates a new coverage map on every request.
+const serverMiddleware = function(app, options) {
+  app.post(WRITE_COVERAGE,
+    bodyParser,
+    (req, res) => {
+      let map = istanbul.libCoverage.createCoverageMap();
+      coverageHandler(map, options, req, res);
     },
     logError);
 };
+
+// Used when app is in ci mode (`ember test`).
+// Collects the coverage on each request and merges it into the coverage map.
+const testMiddleware = function(app, options) {
+  let map = istanbul.libCoverage.createCoverageMap();
+  app.post(WRITE_COVERAGE,
+    bodyParser,
+    coverageHandler.bind(null, map, options),
+    logError);
+};
+
+module.exports = {
+  serverMiddleware,
+  testMiddleware,
+};
diff --git a/lib/coverage-merge.js b/lib/coverage-merge.js
deleted file mode 100644
index 18186376..00000000
--- a/lib/coverage-merge.js
+++ /dev/null
@@ -1,60 +0,0 @@
-'use strict';
-
-var path = require('path');
-var getConfig = require('./config');
-var dir = require('node-dir');
-var Promise = require('rsvp').Promise;
-
-/**
- * Merge together coverage files created when running in multiple threads,
- * for example when being used with ember exam and parallel runs.
- */
-module.exports = {
-  name: 'coverage-merge',
-  description: 'Merge multiple coverage files together.',
-  run: function () {
-    var istanbul = require('istanbul-api');
-    var config = this._getConfig();
-
-    var coverageFolderSplit = config.coverageFolder.split('/');
-    var coverageFolder = coverageFolderSplit.pop();
-    var coverageRoot = this.project.root + '/' + coverageFolderSplit.join('/');
-    var coverageDirRegex = new RegExp(coverageFolder + '_.*');
-
-    let reporter = istanbul.createReporter();
-    reporter.dir = path.join(coverageRoot, coverageFolder);
-    let map = istanbul.libCoverage.createCoverageMap();
-
-    return new Promise(function (resolve, reject) {
-      dir.readFiles(coverageRoot, { matchDir: coverageDirRegex, match: /coverage-final\.json/ },
-        function (err, coverageSummary, next) {
-          if (err) {
-            reject(err);
-          }
-          map.merge(JSON.parse(coverageSummary));
-          next();
-        },
-        function (err) {
-          if (err) {
-            reject(err);
-          }
-
-          if (config.reporters.indexOf('json-summary') === -1) {
-            config.reporters.push('json-summary');
-          }
-
-          reporter.addAll(config.reporters);
-          reporter.write(map);
-          resolve();
-        });
-    });
-  },
-
-  /**
-   * Get project configuration
-   * @returns {Configuration} project configuration
-   */
-  _getConfig: function () {
-    return getConfig(this.project.configPath());
-  }
-};
diff --git a/package.json b/package.json
index 1c58573d..e6a2a81b 100644
--- a/package.json
+++ b/package.json
@@ -38,7 +38,6 @@
     "fs-extra": "^5.0.0",
     "istanbul-api": "^1.1.14",
     "lodash.concat": "^4.5.0",
-    "node-dir": "^0.1.16",
     "rsvp": "^4.8.1",
     "walk-sync": "^0.3.2"
   },
diff --git a/test/fixtures/my-addon/config/coverage.js b/test/fixtures/my-addon/config/coverage.js
index 8e9ccaf6..e3724c51 100644
--- a/test/fixtures/my-addon/config/coverage.js
+++ b/test/fixtures/my-addon/config/coverage.js
@@ -1,3 +1,3 @@
 module.exports = {
-  reporters: ['lcov', 'html', 'text']
+  reporters: ['lcov', 'html', 'text', 'json-summary']
 };
diff --git a/test/fixtures/my-app-with-in-repo-addon/config/coverage.js b/test/fixtures/my-app-with-in-repo-addon/config/coverage.js
index 8e9ccaf6..e3724c51 100644
--- a/test/fixtures/my-app-with-in-repo-addon/config/coverage.js
+++ b/test/fixtures/my-app-with-in-repo-addon/config/coverage.js
@@ -1,3 +1,3 @@
 module.exports = {
-  reporters: ['lcov', 'html', 'text']
+  reporters: ['lcov', 'html', 'text', 'json-summary']
 };
diff --git a/test/fixtures/my-app-with-in-repo-engine/config/coverage.js b/test/fixtures/my-app-with-in-repo-engine/config/coverage.js
index 8e9ccaf6..e3724c51 100644
--- a/test/fixtures/my-app-with-in-repo-engine/config/coverage.js
+++ b/test/fixtures/my-app-with-in-repo-engine/config/coverage.js
@@ -1,3 +1,3 @@
 module.exports = {
-  reporters: ['lcov', 'html', 'text']
+  reporters: ['lcov', 'html', 'text', 'json-summary']
 };
diff --git a/test/fixtures/my-app/config/coverage.js b/test/fixtures/my-app/config/coverage.js
index 8e9ccaf6..e3724c51 100644
--- a/test/fixtures/my-app/config/coverage.js
+++ b/test/fixtures/my-app/config/coverage.js
@@ -1,3 +1,3 @@
 module.exports = {
-  reporters: ['lcov', 'html', 'text']
+  reporters: ['lcov', 'html', 'text', 'json-summary']
 };
diff --git a/test/integration/app-coverage-test.js b/test/integration/app-coverage-test.js
index 57a7fb5f..02ed0b17 100644
--- a/test/integration/app-coverage-test.js
+++ b/test/integration/app-coverage-test.js
@@ -76,14 +76,10 @@ describe('app coverage generation', function() {
     });
   });
 
-  it('uses parallel configuration and merges coverage when merge-coverage command is issued', function() {
+  it('merges coverage when tests are run in parallel', function() {
     expect(dir(`${app.path}/coverage`)).to.not.exist;
-    fs.copySync('tests/dummy/config/coverage-parallel.js', `${app.path}/config/coverage.js`);
     process.env.COVERAGE = true;
     return app.run('ember', 'exam', '--split=2', '--parallel=true').then(function() {
-      expect(dir(`${app.path}/coverage`)).to.not.exist;
-      return app.run('ember', 'coverage-merge');
-    }).then(function() {
       expect(file(`${app.path}/coverage/lcov-report/index.html`)).to.not.be.empty;
       expect(file(`${app.path}/coverage/index.html`)).to.not.be.empty;
       var summary = fs.readJSONSync(`${app.path}/coverage/coverage-summary.json`);
@@ -91,16 +87,13 @@ describe('app coverage generation', function() {
     });
   });
 
-  it('uses nested coverageFolder and parallel configuration and run merge-coverage', function() {
+  it('uses nested coverageFolder', function() {
     var coverageFolder = `${app.path}/coverage/abc/easy-as/123`;
 
     expect(dir(coverageFolder)).to.not.exist;
     fs.copySync('tests/dummy/config/coverage-nested-folder.js', `${app.path}/config/coverage.js`);
     process.env.COVERAGE = true;
     return app.run('ember', 'exam', '--split=2', '--parallel=true').then(function() {
-      expect(dir(coverageFolder)).to.not.exist;
-      return app.run('ember', 'coverage-merge');
-    }).then(function() {
       expect(file(`${coverageFolder}/lcov-report/index.html`)).to.not.be.empty;
       expect(file(`${coverageFolder}/index.html`)).to.not.be.empty;
       var summary = fs.readJSONSync(`${coverageFolder}/coverage-summary.json`);
diff --git a/test/unit/index-test.js b/test/unit/index-test.js
index 3266fe62..7d096f95 100644
--- a/test/unit/index-test.js
+++ b/test/unit/index-test.js
@@ -65,15 +65,39 @@ describe('index.js', function() {
   });
 
   describe('serverMiddleware', function() {
+    var app;
+
     beforeEach(function() {
-      sandbox.stub(Index, 'testemMiddleware');
-      Index.serverMiddleware({
-        app: 'foo-bar'
+      app = {
+        post: sinon.spy()
+      };
+
+      sandbox.stub(Index, 'project').value({
+        root: '/path/to/foo-bar',
+        configPath: sinon.stub().returns('tests/dummy/config/environment.js')
       });
     });
 
-    it('calls testemMiddleware with correct arguments', function() {
-      expect(Index.testemMiddleware.lastCall.args).to.eql(['foo-bar']);
+    describe('when coverage is enabled', function() {
+      beforeEach(function() {
+        sandbox.stub(Index, '_isCoverageEnabled').returns(true);
+        Index.serverMiddleware({ app });
+      });
+
+      it('adds POST endpoint to app', function() {
+        expect(app.post.callCount).to.equal(1);
+      });
+    });
+
+    describe('when coverage is not enabled', function() {
+      beforeEach(function() {
+        sandbox.stub(Index, '_isCoverageEnabled').returns(false);
+        Index.serverMiddleware({ app });
+      });
+
+      it('does not add POST endpoint to app', function() {
+        expect(app.post.callCount).to.equal(0);
+      });
     });
   });
 
diff --git a/tests/dummy/config/coverage-excludes.js b/tests/dummy/config/coverage-excludes.js
index e84a75d7..462c37b2 100644
--- a/tests/dummy/config/coverage-excludes.js
+++ b/tests/dummy/config/coverage-excludes.js
@@ -3,5 +3,6 @@
 module.exports = {
   excludes: [
     '**/utils/my-uncovered-util.js'
-  ]
+  ],
+  reporters: ['lcov', 'html', 'text', 'json-summary']
 };
diff --git a/tests/dummy/config/coverage-nested-folder.js b/tests/dummy/config/coverage-nested-folder.js
index ae5fac98..446eaa4f 100644
--- a/tests/dummy/config/coverage-nested-folder.js
+++ b/tests/dummy/config/coverage-nested-folder.js
@@ -3,5 +3,5 @@
 
 module.exports = {
   coverageFolder: 'coverage/abc/easy-as/123',
-  parallel: true
+  reporters: ['lcov', 'html', 'text', 'json-summary']
 };
diff --git a/tests/dummy/config/coverage-parallel.js b/tests/dummy/config/coverage-parallel.js
deleted file mode 100644
index a33514b6..00000000
--- a/tests/dummy/config/coverage-parallel.js
+++ /dev/null
@@ -1,5 +0,0 @@
-/* eslint-env node */
-
-module.exports = {
-  parallel: true
-};