Add tests for --module esm

test/esm/incorrect.mjs

@@ -0,0 +1,7 @@
+// Convert degrees Celsius to degrees Fahrenheit.
+//
+// > toFahrenheit(0)
+// 32
+export function toFahrenheit(degreesCelsius) {
+  return String (degreesCelsius) + '°F';
+}

test/esm/index.mjs

@@ -0,0 +1,7 @@
+// Convert degrees Celsius to degrees Fahrenheit.
+//
+// > toFahrenheit(0)
+// 32
+export function toFahrenheit(degreesCelsius) {
+  return degreesCelsius * 9 / 5 + 32;
+}

test/index.js

@@ -8,6 +8,9 @@ var Z = require ('sanctuary-type-classes');
 var doctest = require ('..');
 
 
+var esmSupported = Number (process.versions.node.split ('.')[0]) >= 9;
+
+
 //  unlines :: Array String -> String
 function unlines(lines) {
   return lines.reduce (function(s, line) { return s + line + '\n'; }, '');
@@ -57,10 +60,9 @@ function testCommand(command, expected) {
   var status = 0;
   var stdout;
   var stderr = '';
-  var noWarnings = Number (process.versions.node.split ('.')[0]) >= 9;
   try {
     stdout = execSync (
-      command + (noWarnings ? ' --nodejs --no-warnings' : ''),
+      command + (esmSupported ? ' --nodejs --no-warnings' : ''),
       {encoding: 'utf8', stdio: 'pipe'}
     );
   } catch (err) {
@@ -209,6 +211,27 @@ testCommand ('bin/doctest --module commonjs lib/doctest.js', {
   stderr: ''
 });
 
+if (esmSupported) {
+  testCommand ('bin/doctest --module esm test/esm/index.mjs', {
+    status: 0,
+    stdout: unlines ([
+      'running doctests in test/esm/index.mjs...',
+      '.'
+    ]),
+    stderr: ''
+  });
+
+  testCommand ('bin/doctest --module esm test/esm/incorrect.mjs', {
+    status: 1,
+    stdout: unlines ([
+      'running doctests in test/esm/incorrect.mjs...',
+      'x',
+      'FAIL: expected 32 on line 4 (got "0°F")'
+    ]),
+    stderr: ''
+  });
+}
+
 testCommand ('bin/doctest --print test/commonjs/exports/index.js', {
   status: 0,
   stdout: unlines ([