Bupkis comes with a smorgasbord of built-in assertions. Here's some general information about assertions.

Subjects, Phrases, & Parameters

Assertions or expectations have three (3) components when called via expect()/expectAsync().

Subjects

See also: Subject (glossary)

The first argument to expect() is called the subject. The subject is the value being tested. For example, in expect(42, 'to be', 42), the subject is 42.

Phrases

See also: Phrase (glossary)

You may see the term phrase referenced in the documentation. A phrase is a string parameter to the expect() function that decides which assertion to execute. For example, in expect(42, 'to be', 42), the phrase is 'to be'.

Assertions may have multiple phrases that end up executing the same assertion. We call these aliases. For example, the phrases 'to be', 'to equal', and 'is' all execute the same equality assertion.

An assertion has at least one phrase, but may have more than one. For example, the following assertion has two phrases:

expect(
  () => throw new TypeError('Oh no!'),
  'to throw a',
  TypeError,
  'satisfying',
  /Oh no/,
);
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Parameters

See also: Parameter (glossary)

A parameter is considered anything else that's neither a phrase nor a value. This comes into play when an assertion is parametric; this means the assertion expects some extra value to use in some manner.

Typically, a parameter is used for some type of comparison operation, but this is not a requirement.

You will see assertions accepting parameters referred to as parametric assertions.

Assertions without parameters are often called non-parametric assertions or just basic assertions.

Don't confuse parameters and phrases! Just because a string is expected does not mean that it is a phrase. For example, in the assertion:

expect('bruh', 'to be a', 'string');
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…the phrase is 'to be a' and the parameter is 'string'.

Negating Assertions

Any assertion can be negated by prepending the first phrase with not. For example:

expect(42, 'to be', 42);

// negated
expect(42, 'not to be', 42); // AssertionError; 42 is 42
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