Achieve 100% Condition Coverage in Jest

This challenge focuses on understanding and implementing condition coverage within your Jest test suite. Achieving condition coverage ensures that every condition within a decision point (like if statements or logical operators) has been evaluated to both true and false during testing. This leads to more robust and thoroughly tested code.

Problem Description

You are tasked with writing Jest tests for a given TypeScript function. Your primary goal is to ensure that your test suite achieves 100% condition coverage for this function. You will need to analyze the function's logic, identify all conditions, and craft test cases that specifically target each possible outcome of these conditions.

Requirements:

1. Analyze the function: Identify all boolean expressions that determine control flow (e.g., conditions in if, while, for statements, and logical operators like &&, ||).
2. Craft test cases: Write Jest tests that execute code paths covering every true and false evaluation of each individual condition.
3. Verify coverage: Use Jest's coverage reporting capabilities to confirm that 100% condition coverage is achieved.
4. No redundant tests: While thoroughness is key, aim for tests that contribute to condition coverage rather than simply repeating existing paths.

Expected Behavior:

Your Jest tests should, when run with coverage enabled, report 100% condition coverage for the provided function.

Edge Cases to Consider:

• Functions with multiple nested if statements.
• Functions using logical AND (&&) and OR (||) operators.
• Functions where certain conditions might short-circuit the evaluation.

Examples

Let's consider a hypothetical function:

// Function to test (you will be provided with a specific function later)
function processData(value: number, flag: boolean): string {
    if (value > 10 && flag) {
        return "High value and flag is true";
    } else if (value <= 10 || !flag) {
        return "Low value or flag is false";
    } else {
        return "Unexpected state";
    }
}

Example 1: Achieving Condition Coverage

Let's analyze the conditions in processData:

1. value > 10
2. flag
3. value <= 10 (Note: This is the logical negation of value > 10)
4. !flag (Note: This is the logical negation of flag)

To achieve 100% condition coverage, we need to ensure each of these is true and false.

Test Case 1 (Covers value > 10 is true, flag is true): Input: value = 15, flag = true Expected Output: "High value and flag is true" Explanation: value > 10 is true, flag is true.

Test Case 2 (Covers value > 10 is false, flag is false): Input: value = 5, flag = false Expected Output: "Low value or flag is false" Explanation: value > 10 is false. The && short-circuits. value <= 10 is true, !flag is true.

Test Case 3 (Covers value > 10 is false, flag is true): Input: value = 5, flag = true Expected Output: "Low value or flag is false" Explanation: value > 10 is false. value <= 10 is true, !flag is false. This path is taken due to the || operator.

Test Case 4 (Covers value > 10 is true, flag is false): Input: value = 15, flag = false Expected Output: "Low value or flag is false" Explanation: value > 10 is true, but flag is false. The first if condition is false. value <= 10 is false, !flag is true. This path is taken due to the || operator.

Note on Condition vs. Decision Coverage: Achieving 100% condition coverage does not automatically guarantee 100% decision coverage. For example, in Test Case 1, the first if statement's decision (value > 10 && flag) evaluates to true. However, to achieve 100% decision coverage for that if, you might also need a case where the decision evaluates to false (which Test Case 3 covers). This challenge is strictly about condition coverage.

Constraints

• You will be provided with a single TypeScript function to test.
• Your solution must be written in TypeScript.
• You are expected to use Jest for testing.
• Your Jest test suite must achieve 100% condition coverage for the provided function.
• Do not use external libraries for coverage analysis beyond Jest's built-in capabilities.

Notes

• Focus on how individual conditions are evaluated. For a && b, you need to test cases where a is true, a is false, b is true, and b is false. Similarly for a || b.
• Consider how short-circuiting with && and || affects which conditions are evaluated.
• To verify your coverage, run Jest with the --coverage flag: jest --coverage. Examine the generated coverage/lcov-report/index.html file to ensure 100% condition coverage is reported for the target function.
• Think about the simplest set of tests that satisfies the condition coverage requirement. You might not need to test every single possible input combination, but rather strategically chosen ones.