Expectable 1.0.0-alpha

Expectable

Define an expected exception with optional expectations.

Where do I get it

Expectable can be installed using the Nuget package manager

PM> Install-Package Expectable

or the dotnet CLI.

dotnet add package Expectable

How to get started

1. Define an ExpectedException with an exceptionType and optional list of expectations.

   // using Expectable;
   
   ExpectedException expectedException = Expect<ArgumentException>.Where
       .MessageStartWith("value")
       .MessageContains("cannot be", StringComparison.OrdinalIgnoreCase)
       .MessageEndsWith("null");
   

2. Catch exception

   var value = default(string);
   var exception = Assert.Throws(expectedException.Type, () => DoSomething(value));
   
   // void DoSomething(string value)
   // {
   //      if (value == null) 
   //         throw new ArgumentException("value is null");
   //     ...
   // }
   

3. Compare exception

   Assert.Equal(expectedException, exception);
   

   when not equal

   Message:
     Assert.Equal() Failure: Values differ
     Expected: System.ArgumentException where
                 [+] Message starts with "value"
                 [-] Message contains "cannot be" (ComparisonType: OrdinalIgnoreCase)
                 [+] Message ends with "null"
     Actual:   System.ArgumentException: value was not null
                  at Expectable.Tests.ReadmeExamples.ReadmeExamples.DoSomething(String value)
                  at Xunit.Assert.RecordException(Action testCode)
   

Expectations

Expectations allow you to confirm an optional list of expected conditions are fulfilled by the exception.

MessageContains

Checks that the exception message contains a specific string value.

• value : The string to seek.
• comparisonType : One of the enumeration values that determines how the exception message and value are compared. (Default is StringComparison.Ordinal)

MessageContainsCount

Checks that the exception message contains a specific string value a specific number of times.

• expectedCount : The expected number of instances of value within the exception message.
• value : The string to seek.
• comparisonType : One of the enumeration values that determines how the exception message and value are compared. (Default is StringComparison.Ordinal)

MessageEndsWith

Checks that the exception message ends with a specific string value.

• value : The string to compare to the substring at the end of the exception message.
• comparisonType : One of the enumeration values that determines how the exception message and value are compared. (Default is StringComparison.Ordinal)

MessageEquals

Checks that the exception message equals a specific string value.

• value : The string to compare to the exception message..
• comparisonType : One of the enumeration values that determines how the exception message and value are compared. (Default is StringComparison.Ordinal)

MessageMatches

Checks that the exception message matches a specific regular expression pattern.

• pattern : The regular expression pattern to match.
• options : A bitwise combination of the enumeration values that provide options for matching. (Default is RegexOptions.None)

MessageStartsWith

Checks that the exception message starts with a specific string value.

• value : The string to compare to the substring at the start of the exception message.
• comparisonType : One of the enumeration values that determines how the exception message and value are compared. (Default is StringComparison.Ordinal)

ToString()

The value returned is different before and after comparing to a thrown exception. A

Before expectedException.Equals(thrownException)

System.ArgumentException where
      Message starts with "value"
      Message contains "cannot be" (ComparisonType: OrdinalIgnoreCase)
      Message ends with "null"

After expectedException.Equals(thrownException)

System.ArgumentException where
  [+] Message starts with "value"
  [-] Message contains "cannot be" (ComparisonType: OrdinalIgnoreCase)
  [+] Message ends with "null"

[+] expectation matched

[-] expectation not matched

ResetResults()

Removes any previously cached results. The value returned by ToString() is reset to its initial value.

expectedException.ResetResults();

Initialization Alternatives

While using Expect<TException>.Where ... is the most succinct and versatile way to initialize an ExpectedException with expectations, the following alternatives are also available.

Constructor ExpectedException(Type exceptionType, params Expectation[] expectations)

ExpectedException expectedException = new ExpectedException(typeof(ArgumentException),
    new MessageStartsWith("value"),
    new MessageContains("cannot be", StringComparison.OrdinalIgnoreCase),
    new MessageEndsWith("null"));

This is the verbose implementation of Expect<TException>.

Constructor ExpectedException(Exception exception)

ExpectedException expectedException = new ExpectedException(new ArgumentException("value cannot be null"));
// expectedException.Type: typeof(ArgumentException)
// expectedException.Expectations: MessageEquals("value cannot be null")

If the source exception provided was previously thrown, then the value returned by expectedException.ToString will be sourceException.ToString()

Implicit Conversion from an exception instance

ExpectedException expectedException = new ArgumentException("value cannot be null");
// expectedException.Type: typeof(ArgumentException)
// expectedException.Expectations: MessageEquals("value cannot be null")

If the source exception provided was previously thrown, then the value returned by expectedException.ToString will be sourceException.ToString()

Implicit Conversion from exception type

ExpectedException expectedException = typeof(ArgumentException);
// expectedException.Type: typeof(ArgumentException)
// expectedException.Expectations: empty