assertion-arguments: Validate t.plan() argument is a non-negative integer

Fixes #34

Author: sindresorhus

docs/rules/assertion-arguments.md

@@ -10,7 +10,7 @@
 
 Translations: [Français](https://github.com/avajs/ava-docs/blob/main/fr_FR/related/eslint-plugin-ava/docs/rules/assertion-arguments.md)
 
-Enforces passing the right number of arguments to assertion methods like `t.is()`. This rule can optionally also enforce or forbid the use of assertion messages.
+Enforces passing the right number of arguments to assertion methods like `t.is()`. Also validates that `t.plan()` is called with a non-negative integer. This rule can optionally also enforce or forbid the use of assertion messages.
 
 Assertion messages are optional arguments that can be given to any assertion call to improve the error message, should the assertion fail.
 
@@ -25,6 +25,8 @@ test('1', t => {
 	t.is(value); // Not enough arguments
 	t.is(value, expected, message, extra); // Too many arguments
 	t.is(value, expected, false); // Assertion message is not a string
+	t.plan('1'); // Argument is not a non-negative integer
+	t.plan(2.5); // Argument is not a non-negative integer
 });
 
 /* eslint ava/assertion-arguments: ["error", {"message": "always"}] */
@@ -44,6 +46,7 @@ test('3', t => {
 import test from 'ava';
 
 test('1', t => {
+	t.plan(1);
 	t.is(value, expected);
 	t.is(value, expected, message);
 });

rules/assertion-arguments.js

@@ -11,6 +11,7 @@ const MESSAGE_ID_MISSING_MESSAGE = 'missing-message';
 const MESSAGE_ID_FOUND_MESSAGE = 'found-message';
 const MESSAGE_ID_NOT_STRING = 'not-string-message';
 const MESSAGE_ID_OUT_OF_ORDER = 'out-of-order';
+const MESSAGE_ID_PLAN_NOT_INTEGER = 'plan-not-integer';
 
 const expectedNbArguments = {
 	assert: {
@@ -281,6 +282,17 @@ const create = context => {
 				}
 
 				checkArgumentOrder({node, assertion: firstNonSkipMember, context});
+
+				if (firstNonSkipMember === 'plan') {
+					const argument = node.arguments[0];
+					const staticValue = getStaticValue(argument);
+					if (
+						staticValue !== null
+						&& (typeof staticValue.value !== 'number' || !Number.isInteger(staticValue.value) || staticValue.value < 0)
+					) {
+						context.report({node: argument, messageId: MESSAGE_ID_PLAN_NOT_INTEGER});
+					}
+				}
 			}
 
 			if (gottenArguments === nArguments.max && nArguments.min !== nArguments.max) {
@@ -430,6 +442,7 @@ export default {
 			[MESSAGE_ID_FOUND_MESSAGE]: 'Expected no assertion message, but found one.',
 			[MESSAGE_ID_NOT_STRING]: 'Assertion message should be a string.',
 			[MESSAGE_ID_OUT_OF_ORDER]: 'Expected values should come after actual values.',
+			[MESSAGE_ID_PLAN_NOT_INTEGER]: 'Expected `t.plan()` argument to be a non-negative integer.',
 		},
 	},
 };

test/assertion-arguments.js

@@ -12,6 +12,7 @@ const missingError = {messageId: 'missing-message'};
 const foundError = {messageId: 'found-message'};
 const tooFewError = () => ({messageId: 'too-few-arguments'});
 const tooManyError = () => ({messageId: 'too-many-arguments'});
+const planNotIntegerError = {messageId: 'plan-not-integer'};
 const outOfOrderError = (line, column, endLine, endColumn) => ({
 	messageId: 'out-of-order',
 	line, column, endLine, endColumn,
@@ -160,6 +161,11 @@ ruleTester.run('assertion-arguments', rule, {
 	},
 	valid: [
 		testCase(false, 't.plan(1);'),
+		testCase(false, 't.plan(0);'),
+		testCase(false, 't.plan(100);'),
+		testCase(false, 't.plan(n);'),
+		testCase(false, 't.plan(foo());'),
+		testCase(false, 't.plan(a + b);'),
 		testCase(false, 't.assert(true, \'message\');'),
 		testCase(false, 't.deepEqual({}, {}, \'message\');'),
 		testCase(false, 't.fail(\'message\');'),
@@ -380,6 +386,15 @@ ruleTester.run('assertion-arguments', rule, {
 		testCase(false, 't.timeout();', tooFewError()),
 		testCase(false, 't.try();', tooFewError()),
 
+		// Invalid t.plan() argument
+		testCase(false, 't.plan(\'1\');', planNotIntegerError),
+		testCase(false, 't.plan(2.5);', planNotIntegerError),
+		testCase(false, 't.plan(-1);', planNotIntegerError),
+		testCase(false, 't.plan(true);', planNotIntegerError),
+		testCase(false, 't.plan(null);', planNotIntegerError),
+		testCase(false, 't.plan.skip(\'1\');', planNotIntegerError),
+		testCase(false, 'tt.plan(2.5);', planNotIntegerError),
+
 		// Too many arguments
 		testCase(false, 't.plan(1, \'extra argument\');', tooManyError()),
 		testCase(false, 't.assert(true, \'message\', \'extra argument\');', tooManyError()),