Minimal Jest Test Suite Generator

This challenge asks you to create a function that generates a minimal set of Jest tests for a given TypeScript function. The goal is to identify a small, representative set of inputs that, when passed to the target function, will effectively cover its logic and potential edge cases. This is crucial for efficient testing, as it helps avoid redundant tests and ensures core functionality is validated.

Problem Description

You need to implement a TypeScript function, generateMinimalTests, that takes a target TypeScript function and a set of potential input values as arguments. Your function should analyze the target function's behavior with these inputs and return an array of input-output pairs that represent a minimal test suite.

Key Requirements:

• Input Analysis: The function should analyze how the target function behaves with the provided potential inputs. This might involve observing return values, thrown errors, or side effects (though for this challenge, we'll focus on return values and errors).
• Minimality: The returned test suite should be as small as possible while still covering the distinct behaviors observed from the target function. If multiple inputs produce the same output or error, only one representative input-output pair should be included for that behavior.
• Output Format: The function should return an array of objects, where each object has input and expectedOutput properties. expectedOutput can be a value or an error object.
• Error Handling: If the target function throws an error for a given input, this should be captured as the expectedOutput.

Expected Behavior:

Given a target function and a list of potential inputs, generateMinimalTests should produce a list of { input, expectedOutput } pairs. Each pair represents a test case. If two different inputs yield the same outcome (same return value or same error type/message), only one of those input-output pairs should be present in the final minimal test set.

Edge Cases to Consider:

• Functions that always return the same value regardless of input.
• Functions that throw different errors for different invalid inputs.
• Functions that have a mix of valid and invalid input scenarios.
• Functions that handle null or undefined inputs.

Examples

Example 1:

// Target Function
function add(a: number, b: number): number {
  if (typeof a !== 'number' || typeof b !== 'number') {
    throw new Error("Both inputs must be numbers.");
  }
  return a + b;
}

// Potential Inputs
const potentialInputs = [
  [1, 2],
  [5, 10],
  [0, 0],
  [-1, 1],
  ['a', 5], // Invalid input
  [null, 10] // Invalid input
];

// Expected Output of generateMinimalTests(add, potentialInputs)
[
  { input: [1, 2], expectedOutput: 3 },
  { input: [0, 0], expectedOutput: 0 },
  { input: [-1, 1], expectedOutput: 0 },
  { input: ['a', 5], expectedOutput: new Error("Both inputs must be numbers.") },
  { input: [null, 10], expectedOutput: new Error("Both inputs must be numbers.") }
]

// Explanation:
// - [1, 2] -> 3 (basic addition)
// - [5, 10] -> 15 (another valid addition, but produces the same type of output as [1,2], so we can omit it for minimality if we pick [1,2])
// - [0, 0] -> 0 (edge case: zero addition)
// - [-1, 1] -> 0 (edge case: negative numbers)
// - ['a', 5] -> Error("Both inputs must be numbers.")
// - [null, 10] -> Error("Both inputs must be numbers.") (produces the same error as ['a', 5])
// The minimal set includes unique return values and unique error types/messages.
// For simplicity, we'll consider errors with the same message as identical.

Example 2:

// Target Function
function greet(name?: string): string {
  if (!name) {
    return "Hello, stranger!";
  }
  return `Hello, ${name}!`;
}

// Potential Inputs
const potentialInputs = [
  ["Alice"],
  ["Bob"],
  [undefined],
  [null], // Treated as falsy, similar to undefined
  [] // Represents calling with no arguments, same as undefined
];

// Expected Output of generateMinimalTests(greet, potentialInputs)
[
  { input: ["Alice"], expectedOutput: "Hello, Alice!" },
  { input: [undefined], expectedOutput: "Hello, stranger!" }
]

// Explanation:
// - ["Alice"] -> "Hello, Alice!" (named greeting)
// - ["Bob"] -> "Hello, Bob!" (another named greeting, similar behavior to "Alice", so one is sufficient for minimality)
// - [undefined] -> "Hello, stranger!" (no name provided)
// - [null] -> "Hello, stranger!" (falsy, handled same as undefined)
// - [] -> "Hello, stranger!" (no arguments, handled same as undefined)

Constraints

• The target function will be a pure function (no side effects that need to be tracked).
• Inputs to generateMinimalTests will be:
  • targetFn: A function of unknown arity and return type.
  • potentialInputs: An array of arrays, where each inner array represents the arguments to be passed to targetFn.
• The comparison for expectedOutput equality should handle primitives, objects, and Error instances. For errors, compare their messages.
• Performance is not a primary concern, but the approach should be reasonably efficient for a moderate number of potential inputs.

Notes

• You'll need to be able to dynamically call the targetFn with the provided arguments.
• Consider how to represent errors. A good approach is to catch errors and store the Error object itself.
• When comparing outputs, remember that object equality (unless they are the exact same object reference) needs careful consideration. For this problem, assume simple object comparison or that the target function returns primitives or errors.
• Think about how to group inputs that produce the same outcome. A Map or Set could be useful data structures.
• The potentialInputs array is your source of truth for exploring the function's behavior. The generated test set will be a subset of these explorations.