Make the code testable following the review comments

lib/datasource.js

@@ -165,40 +165,50 @@ DataSource.prototype._setupConnector = function () {
     }
 };
 
+// List possible connector module names
+function connectorModuleNames(name) {
+  var names = [name]; // Check the name as is
+  if (!name.match(/^\//)) {
+    names.push('./connectors/' + name); // Check built-in connectors
+    if (name.indexOf('loopback-connector-') !== 0) {
+      names.push('loopback-connector-' + name); // Try loopback-connector-<name>
+    }
+  }
+  return names;
+}
+
+// testable with DI
+function tryModules(names, loader) {
+  var mod;
+  loader = loader || require;
+  for(var m =0; m<names.length; m++) {
+    try {
+      mod = loader(names[m]);
+    } catch (e) {
+     /* ignore */
+    }
+    if (mod) {
+      break;
+    }
+  }
+  return mod;
+}
+
 /*!
  * Resolve a connector by name
  * @param name The connector name
  * @returns {*}
  * @private
  */
-DataSource._resolveConnector = function(name) {
+DataSource._resolveConnector = function(name, loader) {
-  var connector = null;
+  var names = connectorModuleNames(name);
+  var connector = tryModules(names , loader);
   var error = null;
-  if (name.match(/^\//)) {
-    // try absolute path
-    connector = require(name);
-  } else if (existsSync(__dirname + '/connectors/' + name + '.js')) {
-    // try built-in connector
-    connector = require('./connectors/' + name);
-  } else {
-    // try foreign connector
-    try {
-      connector = require(name);
-    } catch(e) {
-      try {
-        if(name.indexOf('loopback-connector-') === -1) {
-          name = 'loopback-connector-' + name;
-          connector = require(name);
-        }
-      } catch (e) {
-        // ignore
-      }
   if(!connector) {
     error = '\nWARNING: LoopBack connector "' + name
-          + '" is not installed,\nso your models would not work, to fix run:\n\n    npm install '
+      + '" is not installed at any of the locations ' + names
-          + name, '\n';
+      + '. To fix, run:\n\n    npm install '
-      }
+      + name + '\n';
-    }
   }
   return {
     connector: connector,

test/loopback-dl.test.js

@@ -445,6 +445,13 @@ describe('Load models with base', function () {
 });
 
 describe('DataSource constructor', function() {
+  // Mocked require
+  var loader = function(name) {
+    return {
+      name: name
+    }
+  };
+
   it('should resolve connector by path', function() {
     var connector = DataSource._resolveConnector(__dirname + '/../lib/connectors/memory');
     assert(connector.connector);
@@ -454,16 +461,28 @@ describe('DataSource constructor', function() {
     assert(connector.connector);
   });
   it('should try to resolve connector by module name starts with loopback-connector-', function() {
+    var connector = DataSource._resolveConnector('loopback-connector-xyz', loader);
+    assert(connector.connector);
+  });
+  it('should try to resolve connector by short module name', function() {
+    var connector = DataSource._resolveConnector('xyz', loader);
+    assert(connector.connector);
+  });
+  it('should try to resolve connector by full module name', function() {
+    var connector = DataSource._resolveConnector('loopback-xyz', loader);
+    assert(connector.connector);
+  });
+  it('should fail to resolve connector by module name starts with loopback-connector-', function() {
     var connector = DataSource._resolveConnector('loopback-connector-xyz');
     assert(!connector.connector);
     assert(connector.error.indexOf('loopback-connector-xyz') !== -1);
   });
-  it('should try to resolve connector by short module name', function() {
+  it('should fail to resolve connector by short module name', function() {
     var connector = DataSource._resolveConnector('xyz');
     assert(!connector.connector);
     assert(connector.error.indexOf('loopback-connector-xyz') !== -1);
   });
-  it('should try to resolve connector by full module name', function() {
+  it('should fail to resolve connector by full module name', function() {
     var connector = DataSource._resolveConnector('loopback-xyz');
     assert(!connector.connector);
     assert(connector.error.indexOf('loopback-connector-loopback-xyz') !== -1);