Assertion

As explained in Web Components in Action

A software assertion is an executable check of an expected condition or property that signals failure when the check does not hold.

assert.equal(doubleNum(2), 4);

How Web Components in Action covers it

How deep it goes

Defines assertions and illustrates expected-value checks, stopping short of explaining assertion-library internals.

Examples

Illustrates arithmetic, a number-doubling function, and slider component values and display state.

What you can do after

Apply Chai assertions to check function results and component state.

How it connects

Connects assertions with Chai, Mocha, browser automation, and testing.

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Also explained in

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  Build Python Web Apps with StreamlitAn assertion is a test check that evaluates an expected condition and reports a failure when the condition is false.
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  Modern Cassert is a C standard library macro that evaluates a runtime condition and reports a diagnostic followed by abnormal termination when the condition is false.
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  Unit Testing Principles, Practices, and PatternsAn assertion is a test statement that checks whether an observed result matches an expected condition.
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  The Art of Unit Testing 3eAn assertion is a test condition that verifies whether an actual result or behavior satisfies an expected truth condition.
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  Modern C, Third Editionassert is a C standard-library assertion macro that evaluates a runtime condition and calls abort when the condition is false.
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  Build Financial Software with Generative AI (From Scratch)An assert statement checks that a condition is true during program execution and signals an assertion failure when it is false.
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  100 Java Mistakes and How to Avoid ThemAn assert statement is a Java language statement that evaluates a boolean condition and raises an assertion failure when the condition is false and assertions are enabled.
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  Effective Platform EngineeringAn assertion is a declarative statement that evaluates as true or false for given data.
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  ASP.NET Core in Action, 3eAn assertion is a test operation that verifies an actual result satisfies an expected condition.
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  Refactoring to RustAn assertion is a program check that verifies a condition and reports failure when the condition is false.
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  Practices of the Python Pro
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  Learn Rust in a Month of Lunches
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  Software Design for Python ProgrammersAn assert statement evaluates a condition and aborts execution when the condition is false.
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  Python How-To

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Related concepts

• lookbehind assertionincludes · A lookbehind assertion is a regular-expression assertion that checks whether a pattern matches before the current position without consuming the checked input.
• lookaheadincludes · A lookahead is a regular-expression assertion that checks whether a pattern matches after the current position without consuming the checked input.
• dynamic bindingconfigured by · A dynamic binding is a value associated with a var for a specific thread, allowing different threads to observe different values.
• testused by · A test is a procedure or check that evaluates behavior using specified inputs or evidence against expected results or criteria.
• exceptionproduces · An exception is a runtime signal or object representing an abnormal condition that interrupts ordinary program flow and may be handled or propagated.
• NDEBUGconfigured by · NDEBUG is a C and C++ preprocessor macro whose definition conventionally disables assertion checks performed by the standard assert mechanism.

This explainer was generated by Manning's knowledge graph from the text of Web Components in Action. The section links point to the parts of the book it draws on.