Fix errors, add dropRequireCacheBeforeRun() option setter

Makefile

@@ -52,7 +52,8 @@ test-browser-tdd:
 test-jsapi:
 	@printf "==> [Test :: JS API]\n"
 	node test/jsapi/index.js
-	node test/jsapi/cache/index.js
+	node test/jsapi/cache/index.simple.js
+	node test/jsapi/cache/index.drop-require-cache.js
 
 test-unit:
 	@printf "==> [Test :: Unit]\n"

lib/mocha.js

@@ -227,7 +227,7 @@ Mocha.prototype.loadFiles = function(fn) {
     suite.emit('post-require', global, file, self);
   });
 
-  if (!process.browser) {
+  if (!process.browser && this.options.dropRequireCache) {
     this._flushRequireCache();
   }
 
@@ -345,6 +345,17 @@ Mocha.prototype.checkLeaks = function() {
   return this;
 };
 
+/**
+ * Delete required files from require.cache before runner starts processing tests
+ *
+ * @return {Mocha}
+ * @api public
+ */
+Mocha.prototype.dropRequireCacheBeforeRun = function() {
+  this.options.dropRequireCache = true;
+  return this;
+};
+
 /**
  * Display long stack-trace on failing
  *

test/jsapi/cache/index.js → test/jsapi/cache/index.drop-require-cache.js

@@ -6,9 +6,11 @@ var testFile = path.resolve(__dirname, 'spec.js');
 var includeFile = path.resolve(__dirname, 'include.js');
 
 var set1 = new Mocha();
+set1.dropRequireCacheBeforeRun();
 set1.addFile(testFile);
 
 var set2 = new Mocha();
+set2.dropRequireCacheBeforeRun();
 set2.addFile(testFile);
 
 set1.run(function () {

test/jsapi/cache/index.simple.js

@@ -0,0 +1,20 @@
+var Mocha = require('../../../')
+  , assert = require('assert')
+  , path = require('path');
+
+var testFile = path.resolve(__dirname, 'spec.js');
+var includeFile = path.resolve(__dirname, 'include.js');
+
+var set1 = new Mocha();
+set1.addFile(testFile);
+
+var set2 = new Mocha();
+set2.addFile(testFile);
+
+set1.run(function () {
+  assert.strictEqual(global[includeFile], 1, 'JSAPI test #1 didn\'t run');
+
+  set2.run(function () {
+    assert.strictEqual(global[includeFile], 1, 'JSAPI test has probably been executed');
+  });
+});