Karma and React, have warnings to cause errors

You can replace the console.warn method with your own and throw when the message provided matches a certain pattern.

let warn = console.warn;console.warn = function(warning) {  if (/(Invalid prop|Failed propType)/.test(warning)) {    throw new Error(warning);  }  warn.apply(console, arguments);};

Small improvements to accepted answer: console.error instead of console.warn as spain-train mentioned, added 'Failed prop type' to regex, as only then it works with React 15.3.1, and made the code more strict eslint friendly.

const error = console.error;console.error = function(warning, ...args) {  if (/(Invalid prop|Failed prop type)/.test(warning)) {    throw new Error(warning);  }  error.apply(console, [warning, ...args]);};

2021 update:

const consoleError = console.error;console.error = function (...args) {  if (/(Invalid prop|Failed propType|Failed .+ type)/.test(args[0])) {    const errorMessage = args.reduce((p, c) => p.replace(/%s/, c));    throw new Error(errorMessage);  }  consoleError.apply(console, args);};

Failed prop type is now Failed %s type: %s%s. It uses string substitutions to write to console. Here is the code in React.