create separate function for path checking

test/unit/coffee/ResourceWriterTests.coffee

@@ -157,6 +157,19 @@ describe "ResourceWriter", ->
 					.calledWith(new Error("resource path is outside root directory"))
 					.should.equal true
 			
-			
+	describe "checkPath", ->
+		describe "with a valid path", ->
+			beforeEach ->
+				@ResourceWriter.checkPath("foo", "bar", @callback)
 
-			
+			it "should return the joined path", ->
+				@callback.calledWith(null, "foo/bar")
+				.should.equal true
+
+		describe "with an invalid path", ->
+			beforeEach ->
+				@ResourceWriter.checkPath("foo", "baz/../../bar", @callback)
+
+			it "should return an error", ->
+				@callback.calledWith(new Error("resource path is outside root directory"))
+				.should.equal true

test/unit/coffee/TikzManager.coffee

@@ -6,6 +6,7 @@ modulePath = require('path').join __dirname, '../../../app/js/TikzManager'
 describe 'TikzManager', ->
 	beforeEach ->
 		@TikzManager = SandboxedModule.require modulePath, requires:
+			"./ResourceWriter": @ResourceWriter = {}
 			"fs": @fs = {}
 			"logger-sharelatex": @logger = {log: () ->}
 
@@ -49,8 +50,13 @@ describe 'TikzManager', ->
 			'''
 			@fs.readFile = sinon.stub().callsArgWith(2, null, @content)
 			@fs.writeFile = sinon.stub().callsArg(3)
+			@ResourceWriter.checkPath = sinon.stub().callsArgWith(2, null, "#{@rootDir}/#{@filename}")
 			@TikzManager.injectOutputFile @rootDir, @filename, @callback
 
+		it "sould check the path", ->
+			@ResourceWriter.checkPath.calledWith(@rootDir, @filename)
+			.should.equal true
+
 		it "should read the file", ->
 			@fs.readFile
 				.calledWith("#{@rootDir}/#{@filename}", "utf8")