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BDD Verify#

The BDD style uses the Verify extension method which wraps RunInMem with assertions defined in a BDD manner using object initializers for some syntactic goodness.

public void Checkout_NewBranch_WithoutBranchFlag_Fails()
    new AppRunner<Git>()
        .Verify(new Scenario
            When = { Args = "checkout lala" },
            Then =
                ExitCode = 1,
                Output = "error: pathspec 'lala' did not match any file(s) known to git"


First, it calls RunInMem and finally it returns an AppRunnerResult, so all options for RunInMem are available in Verify.

Additionally it

  • Captures any exceptions, returns exit code of 1 and outputs the message to the console, as you would see in the shell.
  • Asserts
    • ExitCode... asserts is 0 when ExitCode is specified
    • Console Output
    • TestCaptures

This approach works well with BDD frameworks like SpecFlow where scenarios can be defined in other sources and mapped to code.

More on BDD#

Verify uses the Scenario to follow the Given-When-Then BDD syntax.


Given is the context, which is the AppRunner with configurations. If it helps, when you read new AppRunner<Git>..., replace new with given so it becomes given AppRunner<git>...


When is the action, which is the user input. It always starts with Args, or an ArgsArray if you're testing a scenario the CommandLineStringSplitter doesn't split as expected. In addtiion to args, users can provide piped input and answer prompts

When = 
    Args = $"Knock knock",
    PipedInput = new[] {"orange", "orange you glad I didn't say banana?"},
    OnPrompt = Respond.WithText("rose"),
    OnReadLine = console => "blue"
These are the option available. In practice, you'll only provide one of PipedInput, OnPrompt or OnReadLine. When PipedInput is available, System.Console does not allow Console.Read so you can either have piped input or prompt. OnPrompt registers a delegate for OnReadLine will overrule any OnReadLine delegate provided.

See Testing Piped Input and Testing Propmts for more on those topics.


Then is the assertion, which is generally the console output.

Then =
    ExitCode = 1,
    Output = "exact match",
    OutputContainsTexts = 
        "this", "and this", "and also this"
    OutputNotContainsTexts = 
        "but not this", "or this", "and definitely not this"
    AssertOutput = output => output.Should()...,
    AssertContext = context => 
    Captured =
        new SomeExpectedObject{AnOperand="some-value"}
    AllowUnspecifiedCaptures = true

ExitCode is always checked. If a value is not provided, 0 is used.

Output is the ordered merge of Standard Out and Error Out and expects an exact match. For some output, this can be brittle and contains check is a better choice.

OutputContainsTexts and OutputNotContainsTexts will check for the presence of the strings in the output.

AssertOutput is an Action<string> containing the console output. Use this for more complex assertions.

AssertContext is an Action<CommandContext>. Use this to assert on items in the context.

Captured will check if TestCaptures contains the given objects.

AllowUnspecifiedCaptures when true, TestCaptures can contain objects not specified in Captured. When false, if an object in TestCaptures is not matched by an object in Captured an exception is thrown.


Captured and AllowUnspecifiedCaptures have been obsoleted in favor of AssertContext => ctx.GetCommandInvocation().ParameterValues... and using the Assert library of your choice to verify parameters are wat is expected.

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