hey there:
iam using this module to avoid that --> it converts html templates to js files and put them in the templateCache:
https://github.com/karma-runner/karma-ng-html2js-preprocessor
install it --> add it to you devDependencies in your package.json
after that pu the following in your karma.conf:
preprocessors: {
'app/templates/**/*.html': ['ng-html2js'], // add your template paths
},
ngHtml2JsPreprocessor: { // this changes the name of the files --> e.g. stripping app and add/assets as new path
stripPrefix: 'app',
prependPrefix: '/assets'
}