Meziantou.Framework

Introduction

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Meziantou.Framework.Assertions provides an Assert class for unit tests. Its assertions compare values, text, collections, types, exceptions and events, and their failure messages show the expressions you wrote, the values, and the item or character where they differ. The package also ships analyzers and code fixes that report weak or wrong assertions as you type, such as Assert.True(list.Contains(item)) or an assertion that is never awaited.

A failed assertion throws an AssertionException, which every test framework reports as a failure. The only part tied to a test framework is Assert.XunitSkip, which skips an xUnit.v3 test.

Not the Assert class of your test framework

Meziantou.Framework.Assertions.Assert is a class of its own, not the Assert class of your test framework. Many method names are the same, but the rules are this library's, and one of them is easy to miss: the expected value always comes first, then the actual value, for every assertion, including Contains, StartsWith and EndsWith:

  • Assert.Equal(expected, actual)
  • Assert.Contains(expectedItemOrSubstring, actual)
  • Assert.StartsWith(expectedPrefix, actual)
  • Assert.Matches(pattern, actual)
  • Assert.HasCount(expectedCount, actual)

The analyzer reports a call where the constant is passed as the actual value (MFAS0001). The exceptions are the assertions without an expected value: Assert.Contains(collection, predicate), Assert.All(collection, assertion) and Assert.InRange(actual, low, high) take the value under test first.

To use this Assert class when you write Assert, add a global alias. See Getting started.

What you can do with it

  • Compare values: numbers of different types, strings ignoring case or line endings, floating-point values with a tolerance, dates with a precision, collections item by item. See Equality.
  • Compare objects member by member, regardless of their types, including JSON and XML. See Equivalence.
  • Check text: substrings, prefixes, suffixes and regular expressions. See Text.
  • Check collections: items, subsequences, predicates, counts, single items, per-item assertions, duplicates and sets, on lists, spans, lazy sequences and IAsyncEnumerable<T>. See Collections.
  • Check nulls, types and ranges, and get the value back with the right type. See Nulls, types and ranges.
  • Check exceptions and events, synchronous or asynchronous. See Exceptions and Events.
  • Read the failure messages and control how much of a value they show. See Failure messages.
  • Write better assertions with the help of the analyzers. See Analyzer rules.
  • Check the architecture of an application, such as the dependencies between layers and namespaces, with Assert.Architecture. See Architecture.

Namespace

Assert, AssertionException, EquivalentOptions, FormatterOptions and RaisedEvent<TEventArgs> are in the Meziantou.Framework.Assertions namespace.

Next steps