eslint-plugin-no-multiple-returns/tests/no-multiple-returns.test.ts

An ESLint plugin to enforce a single `return` statement per function, encouraging clearer and more maintainable code.

import { describe, it } from "vitest";
import { RuleTester } from "eslint";
import rule from "../src/rules/no-multiple-returns";

// ESLint RuleTester needs to be configured properly for Vitest
const ruleTester = new RuleTester({
  languageOptions: {
    ecmaVersion: 2020,
    sourceType: "module",
  },
});

describe("no-multiple-returns", () => {
  it("should validate the rule", () => {
    ruleTester.run("no-multiple-returns", rule, {
      valid: [
        `function singleReturn() { return 1; }`,
        `const fn = () => { return 42; }`,
        `const concise = () => 123;`,
        // Test case: nested function with return should not count as multiple returns
        `const TimerComponent = () => {
          const [seconds, setSeconds] = useState(0);
          useEffect(() => {
            const intervalId = setInterval(() => {
              setSeconds((prev) => prev + 1);
            }, 1000);
            return () => {
              clearInterval(intervalId);
              console.log('Timer cleaned up');
            };
          }, []);
          return React.createElement('div', null, 'Timer: ' + seconds + 's');
        };`,
        // Test case: nested React component should not count as multiple returns
        `const ParentComponent = () => {
          const NestedComponent = () => {
            return React.createElement('span', null, 'Nested');
          };
          return React.createElement('div', null, React.createElement(NestedComponent, null));
        };`,
        // Test case: function with conditional returns inside React component (should be valid)
        `const ConditionalComponent = () => {
          const helper = (condition) => {
            if (condition) return 'yes';
            return 'no';
          };
          return React.createElement('div', null, helper(true));
        };`,
        // Test case: complex nested scenario with useEffect and nested components
        `const ComplexComponent = () => {
          const [state, setState] = useState(false);
          
          useEffect(() => {
            const cleanup = () => {
              if (state) return 'cleanup1';
              return 'cleanup2';
            };
            return cleanup;
          }, [state]);
          
          const NestedComp = () => {
            return React.createElement('span', null, 'nested');
          };
          
          return React.createElement('div', null, React.createElement(NestedComp, null));
        };`,
      ],
      invalid: [
        {
          code: `function bad() { if (x) return 1; return 2; }`,
          errors: [{ message: /has 2 return statements/ }],
        },
        {
          code: `const bad = () => { if (x) return 1; return 2; };`,
          errors: [{ message: /has 2 return statements/ }],
        },
      ],
    });
  });
});