test: re-use static build directory for caching between test runs

lib/commands/test.js

@@ -4,6 +4,7 @@ var command = {
   builder: {},
   run: function (options, done) {
     var OS = require("os");
+    var path = require('path');
     var dir = require("node-dir");
     var temp = require("temp");
     var Config = require("truffle-config");
@@ -43,12 +44,31 @@ var command = {
       dir.files(config.test_directory, callback);
     };
 
+    function getTestTempDir(cb) {
+      var tempDir = path.join(config.working_directory, '.tmp');
+      var testDir = path.join(tempDir, 'test');
+
+      try {
+        if (!fs.existsSync(tempDir)) {
+          fs.mkdirSync(tempDir);
+        }
+
+        if (!fs.existsSync(testDir)) {
+          fs.mkdirSync(testDir);
+        }
+
+        cb(null, testDir);
+      } catch (err) {
+        cb(err);
+      }
+    }
+
     getFiles(function(err, files) {
       files = files.filter(function(file) {
         return file.match(config.test_file_extension_regexp) != null;
       });
 
-      temp.mkdir('test-', function(err, temporaryDirectory) {
+      getTestTempDir(function (err, temporaryDirectory) {
         if (err) return done(err);
 
         function cleanup() {