diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -267,6 +267,7 @@
     'ArcanistXMLLinterTestCase' => 'lint/linter/__tests__/ArcanistXMLLinterTestCase.php',
     'ArcanistXUnitTestResultParser' => 'unit/parser/ArcanistXUnitTestResultParser.php',
     'CSharpToolsTestEngine' => 'unit/engine/CSharpToolsTestEngine.php',
+    'MochaTestEngine' => 'unit/engine/MochaTestEngine.php',
     'NoseTestEngine' => 'unit/engine/NoseTestEngine.php',
     'PhpunitTestEngine' => 'unit/engine/PhpunitTestEngine.php',
     'PhpunitTestEngineTestCase' => 'unit/engine/__tests__/PhpunitTestEngineTestCase.php',
@@ -540,6 +541,7 @@
     'ArcanistXMLLinterTestCase' => 'ArcanistLinterTestCase',
     'ArcanistXUnitTestResultParser' => 'Phobject',
     'CSharpToolsTestEngine' => 'XUnitTestEngine',
+    'MochaTestEngine' => 'ArcanistUnitTestEngine',
     'NoseTestEngine' => 'ArcanistUnitTestEngine',
     'PhpunitTestEngine' => 'ArcanistUnitTestEngine',
     'PhpunitTestEngineTestCase' => 'PhutilTestCase',
diff --git a/src/unit/engine/MochaTestEngine.php b/src/unit/engine/MochaTestEngine.php
new file mode 100644
--- /dev/null
+++ b/src/unit/engine/MochaTestEngine.php
@@ -0,0 +1,206 @@
+<?php
+/**
+ * Uses mocha (https://mochajs.org/) to test Javascript code.
+ * Uses istanbul (https://gotwarlost.github.io/istanbul/) to cover Javascript
+ * code.
+ *
+ * Assumes that when modifying a file with a path like `SomeDir/SomeFile.js`,
+ * that the unit test  that verifies the functionality of `SomeFile` is
+ * located at `SomeDir/__tests__/SomeFile-test.js`.
+ *
+ * @concrete-extensible
+ */
+final class MochaTestEngine extends ArcanistUnitTestEngine {
+
+    private $projectRoot;
+
+    /**
+     * Return the name of the test engine.
+     * So it can be used in ArcanistConfigurationDrivenUnitTestEngine later.
+     */
+    public function getEngineConfigurationName() {
+        return 'mocha';
+    }
+
+    /**
+     * This test engine supports running all tests.
+     */
+    protected function supportsRunAllTests() {
+        return true;
+    }
+
+    /**
+     * Main entry point for the test engine. Determines what files changed
+     * and test based on the files that have changed.
+     * @return array Array of test results.
+     * @throws ArcanistNoEffectException
+     * @throws CommandException
+     */
+    public function run() {
+        /*
+         * Determine whether it shall run all the test or more precisely the
+         * modified file
+         *
+         */
+        if (!$this->getRunAllTests()) {
+            $pattern_tests = $this->getAllTestsPattern();
+        } else {
+            $pattern_tests = $this->getGranularTestsPattern();
+        }
+        /*
+         * Throw an error if there is no test that can be run
+         */
+        if (!$pattern_tests) {
+            throw new ArcanistNoEffectException(pht('No tests to run.'));
+        }
+        /*
+         * Retrieve working copy and project root path
+         */
+        $working_copy = $this->getWorkingCopy();
+        $this->$projectRoot = $working_copy->getProjectRoot();
+        /*
+         * Create new temp-file paths to receive junit test result
+         * and lcov coverage result only if coverage is activated.
+         */
+        $junit_tmp = new TempFile();
+        $cover_tmp =  null;
+        if ($this->getEnableCoverage() !== false) {
+            $cover_tmp = Filesystem::resolvePath('./coverage/lcov.info',
+                $this->projectRoot);
+        }
+
+        $future = $this->buildTestFuture($pattern_tests, $junit_tmp);
+        list($err, $stdout, $stderr) = $future->resolve();
+
+        /*
+         * Check that the future output desired files
+         */
+        if (!Filesystem::pathExists($junit_tmp)) {
+            throw new CommandException(
+                pht('Testing Command failed with error #%s!', $err),
+                $future->getCommand(),
+                $err,
+                $stdout,
+                $stderr);
+        }
+        if ($this->getEnableCoverage() !== false) {
+            if (!Filesystem::pathExists($cover_tmp)) {
+                throw new CommandException(
+                    pht('Coverage Command failed with error #%s!', $err),
+                    $future->getCommand(),
+                    $err,
+                    $stdout,
+                    $stderr);
+            }
+        }
+
+        return $this->parseTestResults($junit_tmp, $cover_tmp);
+    }
+
+    /**
+     * Return pattern for retrieving test files
+     * If special pattern isn't set in configuration file, it is defaulted
+     */
+    private function getAllTestsPattern() {
+        $pattern = $this->getConfigurationManager()
+            ->getConfigFromAnySource('unit.mocha.pattern');
+        if (!$pattern) {
+            $pattern = '/tests/*.spec.js';
+        }
+        return $pattern;
+    }
+
+    /**
+     * This test engine supports running all tests.
+     */
+    private function getGranularTestsPattern() {
+        // TODO : build something really granular.
+        return $this->getAllTestsPattern();
+    }
+
+
+    private function buildTestFuture($pattern_tests, $junit_tmp) {
+        $cmd_line = csprintf(
+            'MOCHA_FILE=%s'.
+            'mocha test --reporter mocha-junit-reporter -u exports -R %s',
+            $junit_tmp);
+
+        if ($this->getEnableCoverage() !== false) {
+            $cmd_line = csprintf(
+                'MOCHA_FILE=%s'.
+                'ISTANBUL_REPORTERS=cobertura'.
+                'istanbul cover _mocha'.
+                '-- -u exports -R %s',
+                $junit_tmp);
+        }
+
+        return new ExecFuture('%C %s', $cmd_line, $pattern_tests);
+    }
+
+    private function parseTestResults($junit_tmp, $cover_tmp) {
+        $parser = new ArcanistXUnitTestResultParser();
+        $results = $parser->parseTestResults(Filesystem::readFile($junit_tmp));
+        if ($this->getEnableCoverage() !== false) {
+            $coverage = $this->readCoverage($cover_tmp);
+            foreach ($results as $result) {
+                $result->setCoverage($coverage);
+            }
+        }
+        return $results;
+    }
+
+    /**
+     * TODO: This is copied from @{class:NoseTestEngine}.
+     * I didn't ever try to understand what is going on.
+     */
+    public function readCoverage($cover_file) {
+        $coverage_dom = new DOMDocument();
+        $coverage_dom->loadXML(Filesystem::readFile($cover_file));
+
+        $reports = array();
+        $classes = $coverage_dom->getElementsByTagName('class');
+
+        foreach ($classes as $class) {
+            $path = $class->getAttribute('filename');
+            $root = $this->getWorkingCopy()->getProjectRoot();
+
+            if (!Filesystem::isDescendant($path, $root)) {
+                continue;
+            }
+
+            // get total line count in file
+            $lines_list = phutil_split_lines(Filesystem::readFile($path));
+            $line_count = count($lines_list);
+
+            $coverage = '';
+            $start_line = 1;
+            $lines = $class->getElementsByTagName('line');
+            for ($ii = 0; $ii < $lines->length; $ii++) {
+                $line = $lines->item($ii);
+
+                $next_line = intval($line->getAttribute('number'));
+                for ($start_line; $start_line < $next_line; $start_line++) {
+                    $coverage .= 'N';
+                }
+
+                if (intval($line->getAttribute('hits')) == 0) {
+                    $coverage .= 'U';
+                } else if (intval($line->getAttribute('hits')) > 0) {
+                    $coverage .= 'C';
+                }
+
+                $start_line++;
+            }
+
+            if ($start_line < $line_count) {
+                foreach (range($start_line, $line_count) as $line_num) {
+                    $coverage .= 'N';
+                }
+            }
+
+            $reports[$path] = $coverage;
+        }
+
+        return $reports;
+    }
+}