feat: implement prefer-expect-assertions rule (#43)

* feat: implement missing_expect_assertions_call rule

Intial code for missing_expect_assertions_call rule

* style: lint auto fix

* refactor: enhance missing_expect_assertions_call rule

Report error when expect.assertions() call is present but the argument provided is not a number

* refactor: enhance missing_expect_assertions_call rule

Rule will not report any error, if expect.hasAssertions() call is present. After this change, either expect.hasAssertions() or expect.assertions({number of assertions}) is required to pass the rule

* refactor(readability): improving missing-expect-assertions-call rule msg

* refactor: missing-expect-assertions-call rule rename

Rename missing-expect-assertions-call to prefer-expect-assertions

* refactor: remove unnecessary return

* fix: do not add the rule to recommended

* refactor: update test message

* test: adding missing tests and refactoring

Author: tushardhole

index.js

@@ -8,6 +8,7 @@ const preferToBeNull = require('./rules/prefer_to_be_null');
 const preferToBeUndefined = require('./rules/prefer_to_be_undefined');
 const preferToHaveLength = require('./rules/prefer_to_have_length');
 const validExpect = require('./rules/valid_expect');
+const preferExpectAssertions = require('./rules/prefer_expect_assertions');
 
 const snapshotProcessor = require('./processors/snapshot-processor');
 
@@ -62,5 +63,6 @@ module.exports = {
     'prefer-to-be-undefined': preferToBeUndefined,
     'prefer-to-have-length': preferToHaveLength,
     'valid-expect': validExpect,
+    'prefer-expect-assertions': preferExpectAssertions,
   },
 };

rules/__tests__/prefer_expect_assertions.test.js

@@ -0,0 +1,91 @@
+'use strict';
+
+const RuleTester = require('eslint').RuleTester;
+const rules = require('../..').rules;
+
+const ruleTester = new RuleTester({
+  parserOptions: {
+    ecmaVersion: 6,
+  },
+});
+
+const expectedMsg =
+  'Every test should have either `expect.assertions(<number of assertions>)` or `expect.hasAssertions()` as its first expression';
+
+ruleTester.run('prefer-expect-assertions', rules['prefer-expect-assertions'], {
+  invalid: [
+    {
+      code: 'it("it1", () => {})',
+      errors: [
+        {
+          message: expectedMsg,
+        },
+      ],
+    },
+    {
+      code: 'it("it1", () => { foo()})',
+      errors: [
+        {
+          message: expectedMsg,
+        },
+      ],
+    },
+    {
+      code:
+        'it("it1", function() {' +
+        '\n\t\t\tsomeFunctionToDo();' +
+        '\n\t\t\tsomeFunctionToDo2();\n' +
+        '\t\t\t})',
+      errors: [
+        {
+          message: expectedMsg,
+        },
+      ],
+    },
+    {
+      code: 'it("it1", function() {var a = 2;})',
+      errors: [
+        {
+          message: expectedMsg,
+        },
+      ],
+    },
+    {
+      code: 'it("it1", function() {expect.assertions();})',
+      errors: [
+        {
+          message: expectedMsg,
+        },
+      ],
+    },
+    {
+      code: 'it("it1", function() {expect.assertions(1,2);})',
+      errors: [
+        {
+          message: expectedMsg,
+        },
+      ],
+    },
+    {
+      code: 'it("it1", function() {expect.assertions("1");})',
+      errors: [
+        {
+          message: expectedMsg,
+        },
+      ],
+    },
+  ],
+
+  valid: [
+    {
+      code: 'test("it1", () => {expect.assertions(0);})',
+    },
+    'test("it1", function() {expect.assertions(0);})',
+    'test("it1", function() {expect.hasAssertions();})',
+    'it("it1", function() {expect.assertions(0);})',
+    'it("it1", function() {\n\t\t\texpect.assertions(1);' +
+      '\n\t\t\texpect(someValue).toBe(true)\n' +
+      '\t\t\t})',
+    'test("it1")',
+  ],
+});

rules/prefer_expect_assertions.js

@@ -0,0 +1,81 @@
+'use strict';
+
+const ruleMsg =
+  'Every test should have either `expect.assertions(<number of assertions>)` or `expect.hasAssertions()` as its first expression';
+
+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 isTestOrItFunction = node => {
+  return (
+    node.type === 'CallExpression' &&
+    node.callee &&
+    (node.callee.name === 'it' || node.callee.name === 'test')
+  );
+};
+
+const getFunctionFirstLine = functionBody => {
+  return functionBody[0] && functionBody[0].expression;
+};
+
+const isFirstLineExprStmt = functionBody => {
+  return functionBody[0] && functionBody[0].type === 'ExpressionStatement';
+};
+
+const getTestFunctionBody = node => {
+  try {
+    return node.arguments[1].body.body;
+  } catch (e) {
+    return undefined;
+  }
+};
+
+const reportMsg = (context, node) => {
+  context.report({
+    message: ruleMsg,
+    node,
+  });
+};
+
+module.exports = context => {
+  return {
+    CallExpression(node) {
+      if (isTestOrItFunction(node)) {
+        const testFuncBody = getTestFunctionBody(node);
+        if (testFuncBody) {
+          if (!isFirstLineExprStmt(testFuncBody)) {
+            reportMsg(context, node);
+          } else {
+            const testFuncFirstLine = getFunctionFirstLine(testFuncBody);
+            if (!isExpectAssertionsOrHasAssertionsCall(testFuncFirstLine)) {
+              reportMsg(context, node);
+            }
+          }
+        }
+      }
+    },
+  };
+};