Test Equal (Grade A) logo

Test Equal (Grade A)Security-tested data-ai skill for Claude AI. Grade A. When testing Either values, compare the value directly with shouldBe instead of checking isLeft, so test failures show the actual value. Use when

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Daniel NikulshynReviewed by Daniel Nikulshyn·Updated July 2026

Overview

When testing Either values, compare the value directly with shouldBe instead of checking isLeft, so test failures show the actual value. This skill is useful when writing or reviewing Haskell test code that asserts on Either or similar values. Specifically, when Either's value has instances of Show and Eq, comparing the value directly can be done simply, for example, by comparing it with Left "expected error". Alternatively, even when Eq's instance is not available, using a function that checks the actual behavior is preferable to passing isLeft's result to shouldBe.

Key features

  • Direct value comparison
  • Improved test failure messages
  • Support for Either values

Pricing

Model
Free
Category
Skills
Rating
No reviews yet

Use cases

Testing Either Values

Use this skill when testing Haskell code that returns Either values to ensure detailed test failure messages.

Reviewing Test Code

Use this skill when reviewing test code that asserts on Either or similar values to improve code quality.

Pros & Cons

Pros

  • Provides detailed test failure information
  • Allows for direct comparison of Either values
  • Improves test code readability

Cons

  • Limited to testing Either values
  • Requires Either values to be instances of Show and Eq

Reviews

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Q&A

What are the limitations of using Test Equal?

The skill only applies to Either-like types and requires the values to be instances of Show (and preferably Eq). It cannot be used for arbitrary data types outside this pattern.

Asked by Noelia Campos · Oct 12, 2025

Do I need custom Show or Eq instances for my Either values?

If your Either values implement Show and Eq, you can compare them directly with shouldBe. If Eq is unavailable, use a function that inspects the behavior rather than isLeft.

Asked by Hana Kobayashi · Oct 2, 2025

What types of tests does Test Equal support?

Test Equal is designed for Haskell testing of Either values, allowing direct comparison with expected Left or Right values and improving failure messages.

Asked by Olamide Fashola · Sep 27, 2025

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