eslint-plugin-jest/lib/rules/prefer-expect-assertions.js

Eslint rules for Jest

'use strict';

const _require = require('./util'),
      getDocsUrl = _require.getDocsUrl;

const validateArguments = expression => {
  return expression.arguments && expression.arguments.length === 1 && Number.isInteger(expression.arguments[0].value);
};

const isExpectAssertionsOrHasAssertionsCall = expression => {
  try {
    const expectAssertionOrHasAssertionCall = expression.type === 'CallExpression' && expression.callee.type === 'MemberExpression' && expression.callee.object.name === 'expect' && (expression.callee.property.name === 'assertions' || expression.callee.property.name === 'hasAssertions');

    if (expression.callee.property.name === 'assertions') {
      return expectAssertionOrHasAssertionCall && validateArguments(expression);
    }

    return expectAssertionOrHasAssertionCall;
  } catch (e) {
    return false;
  }
};

const getFunctionFirstLine = functionBody => {
  return functionBody[0] && functionBody[0].expression;
};

const isFirstLineExprStmt = functionBody => {
  return functionBody[0] && functionBody[0].type === 'ExpressionStatement';
};

const reportMsg = (context, node) => {
  context.report({
    messageId: 'haveExpectAssertions',
    node
  });
};

module.exports = {
  meta: {
    docs: {
      url: getDocsUrl(__filename)
    },
    messages: {
      haveExpectAssertions: 'Every test should have either `expect.assertions(<number of assertions>)` or `expect.hasAssertions()` as its first expression'
    }
  },

  create(context) {
    return {
      'CallExpression[callee.name=/^(it|test)$/][arguments.1.body.body]'(node) {
        const testFuncBody = node.arguments[1].body.body;

        if (!isFirstLineExprStmt(testFuncBody)) {
          reportMsg(context, node);
        } else {
          const testFuncFirstLine = getFunctionFirstLine(testFuncBody);

          if (!isExpectAssertionsOrHasAssertionsCall(testFuncFirstLine)) {
            reportMsg(context, node);
          }
        }
      }

    };
  }

};