XBehave – Exporting your Given, Then, When to html

For a project in my day job we have been using the excellent XBehave for our integration tests. I love XBehave in that it lets you use a Given, When, Then syntax over the top of XUnit. There are a couple of issues with XBehave that I have yet to find a neat solution for (unless I am missing something please tell me if this is the case). The issues are

1) There is not a nice way to extract the Given, When, Then gherkin syntax out of the C# assembly for reporting
2) The runner treats each step in the scenario as a separate test

To solve these to problems I am writing an open source parser that takes the xml produced by the XUnit console runner and parses it to a C# model. I can then use razor to render these models as html and spit out the resultant html.

This will mean that I can take the html and post it up to a wiki so every time a new build runs the tests it would be able to update the wiki with the latest set of tests that are in the code and even say whether the tests pass or fail. Allowing a business/product owner to review the tests, see which pieces of functionality are covered and which features have been completed.

To this end I have created the XUnit.Reporter github repository. This article will cover the parsing of the xml into a C# model.

A neat class that I am using inside the XUnit.Reporter is the AssemblyResource class. This class allows easy access to embedded assembly resources. Which means that I can run the XUnit console runner for a test, take the resultant output and add it to the test assembly as an embedded resource. I can then use the AssemblyResource class to load back the text from the xml file by using the following line of code:

AssemblyResource.InAssembly(typeof(ParserScenarios).Assembly, "singlepassingscenario.xml").GetText())

To produce the test xml files for the tests I simply set up a console app, added XBehave and then created a test in the state I wanted for example a single scenario that passes. I then ran the XUnit console runner with the -xml flag set to produce the xml output. I then copied the xml output to a test file and named it accordingly.

The statistics for the assembly model and test collection model are not aligned to what I think you would want from an XBehave test. For example if you have this single XBehave test:


public class MyTest
{
[Scenario]
public void MyScenario()
{
"Given something"
._(() => { });

"When something"
._(() => { });

"Then something should be true"
._(() => { });

"And then another thing"
._(() => { });
}
}

Then the resultant xml produced by the console runner is:

<?xml version="1.0" encoding="utf-8"?>
<assemblies>
<assembly name="C:\projects\CommandScratchpad\CommandScratchpad\bin\Debug\CommandScratchpad.EXE" environment="64-bit .NET 4.0.30319.42000 [collection-per-class, parallel (2 threads)]" test-framework="xUnit.net 2.1.0.3179" run-date="2017-01-27" run-time="17:16:00" config-file="C:\projects\CommandScratchpad\CommandScratchpad\bin\Debug\CommandScratchpad.exe.config" total="4" passed="4" failed="0" skipped="0" time="0.161" errors="0">
<errors />
<collection total="4" passed="4" failed="0" skipped="0" name="Test collection for RandomNamespace.MyTest" time="0.010">
<test name="RandomNamespace.MyTest.MyScenario() [01] Given something" type="RandomNamespace.MyTest" method="MyScenario" time="0.0023842" result="Pass" />
<test name="RandomNamespace.MyTest.MyScenario() [02] When something" type="RandomNamespace.MyTest" method="MyScenario" time="0.0000648" result="Pass" />
<test name="RandomNamespace.MyTest.MyScenario() [03] Then something should be true" type="RandomNamespace.MyTest" method="MyScenario" time="0.0000365" result="Pass" />
<test name="RandomNamespace.MyTest.MyScenario() [04] And then another thing" type="RandomNamespace.MyTest" method="MyScenario" time="0.000032" result="Pass" />
</collection>
</assembly>
</assemblies>

If you look carefully at the xml you will notice a number of things which are counter-intuative. Firstly look at the total in the assembly element it says 4, when we only had a single test. This is because the runner is considering each step to be a separate test. The same goes for the other totals and the totals in the collection element. The next thing that you will notice is that the step names in the original test have had a load of junk added to the front of them.

In the parser I produce a model with the results that I would expect. So for the above xml it I produce an assembly model with a total of 1 test, 1 passed, 0 failed, 0 skipped and 0 errors. Which I think makes much more sense for XBehave tests.

Feel free to clone the repository and look through the parsing code (warning it is a big ugly). Next time I will be talking through the remainder of this app which is rendering the test results to html using razor.

SqlJuxt – Using partial function application to improve the API

After I got all of the tests passing for creating and comparing primary keys on a table I looked back at the code and decided that it had a bit of a smell to it.  Consider the following code snippet:

let private withPrimaryKey columns table isClustered =
    let cs = getColumnsByNames columns table
    {table with primaryKey = Some {name = sprintf "PK_%s" table.name; columns = cs; isClustered = isClustered}}
            
let WithClusteredPrimaryKey columns table =
    withPrimaryKey columns table true

let WithNonClusteredPrimaryKey columns table =
    withPrimaryKey columns table false

The isClustered parameter is of type bool. This in itself does not feel quite right. You can see what I mean when you look at the implementation of WithClusteredPrimaryKey or WithNonClusteredPrimaryKey. The line reads “withPrimaryKey columns table false”. It is obvious what all of those parameters are except the bool at the end. What does false mean?

Clearly this would be much better if it was self describing which we can easily do in F# using a discriminate union. By defining one like so:

type Clustering = CLUSTERED | NONCLUSTERED

The other part that was causing the code to smell but was perhaps less obvious was the order of the parameters. As described by the excellent post on F# for fun and profit on partial function application the order of your parameters is very important. In the builder functions shown above table is always placed last this means you do not need to mention it when using the script builder API, for example:

let rightTable = CreateTable "DifferentKeyTable"
                        |> WithInt "Column1"
                        |> WithInt "Column2" 
                        |> WithInt "Column3" 
                        |> WithClusteredPrimaryKey [("Column1", ASC); ("Column2", ASC)]
                        |> Build 

Notice how the table parameter does not need to be explicitly passed around. You would have to pass this if it was not the last parameter.

So we know that the order is important if we look at the with primary key functions we can see that the isClustered parameter being last stops us from using partial application so when we define the two methods to create a non clustered and clustered primary key we have to explicitly pass all of the parameters.

Here is the redesigned code of the WithPrimaryKey methods on the TableBuilder API:

let WithPrimaryKey clustering columns table =
    let cs = getColumnsByNames columns table
    {table with primaryKey = Some {name = sprintf "PK_%s" table.name; columns = cs; Clustering = clustering}}
              
let WithClusteredPrimaryKey = WithPrimaryKey CLUSTERED
let WithNonClusteredPrimaryKey = WithPrimaryKey NONCLUSTERED

Notice how much cleaner these three methods are now. By moving the clustering parameter to the start and using a discriminate union instead of a bool we have achieved two things. Firstly, the code is now self documenting as we are not passing true or false but instead passing CLUSTERED or NONCLUSTERED. Secondly because the clustering parameter is now first we can use the magic of partial function application to define WithClusteredPrimaryKey and WithNonClusteredPrimaryKey. Those two methods simply bake in whether the key is clustered or not and then leave you to fill in the rest of the parameters.

I really love how F# allows you to write beautiful code like this. I’m still learning to write functional code and am really enjoying the experience. Any feedback comments are welcome so please keep them coming.

If you want to check out the full source code and delve deeper feel free to check out the SqlJuxt GitHub repository.

SqlJuxt – Building primary keys on a table

There were a few interesting design decisions I had to make when designing the code to script a primary key on a table. Before I dive into them I think it is good to see the finished code, here is a test that uses the TableBuilder to create a clustered primary key on a table:

[<Fact>]
let ``should be able to build a table with a clustered primary key on a mulitple columns``() =
    CreateTable "RandomTableName"
        |> WithInt "MyKeyColumn"
        |> WithInt "SecondKeyColumn"
        |> WithVarchar "ThirdCol" 50
        |> WithVarchar "ForthCol" 10
        |> WithClusteredPrimaryKey [("MyKeyColumn", ASC); ("SecondKeyColumn", DESC); ("ThirdCol", DESC)]
        |> Build
        |> should equal @"CREATE TABLE [dbo].[RandomTableName]( [MyKeyColumn] [int] NOT NULL, [SecondKeyColumn] [int] NOT NULL, [ThirdCol] [varchar](50) NOT NULL, [ForthCol] [varchar](10) NOT NULL )
GO

ALTER TABLE [dbo].[RandomTableName] ADD CONSTRAINT [PK_RandomTableName] PRIMARY KEY CLUSTERED ([MyKeyColumn] ASC, [SecondKeyColumn] DESC, [ThirdCol] DESC)
GO"

What I like about this code is that just from reading it, it is obvious what the code will do. It will create a create table script with 4 columns with a clustered primary key on 3 of those cloumns.

I decided to go with the approach to take the minimal amount of arguments possible in order to define the primary key. Those being the list of column names and sort order of the columns that you want as a primary key. Originally I thought about allowing the user to specify the primary key name but actually this just adds noise to the code. One can be generated using the convention “PK_” + tableName. Also why make the user think about the name for the primary key when all we really care about is that there is a primary key there and that it has a unique name.

I love the way that in f# you can use discriminate unions to represent states to make the code easy to read and work with. In the above example I could have taken many approaches to specify the column sort order such as using a bool to say whether or not the column is ascending. However, if I had gone with that approach then when calling the code you would have ended up with “columnName true” or “columnName false”. This already feels horrible as just from reading the code you do not know what the true or false means. By defining a discriminate union of ASC/DESC you can immediately tell what the parameter is and what it is doing.

The primary key is defined as a constraint as the following type:

type Constraint = {name: string; columns: (Column * SortDirection)  list; isClustered: bool}

Then the table type has been extended to add a Constraint as a primary key using the option type. As a table may or may not have a primary key. It is nice that we can use Option to represent this rather than having to rely on null like we would in an imperative language.

The hardest part to making this work is taking the list of (String * SortDirection) that the WithClusteredPrimaryKey function takes and turning that in to a list of (Column * SortDirection). This is done using the following function:

let private getColumnsByNames (columnNames: (string * SortDirection) list) table =
            columnNames |> List.map(fun (c,d) -> let column = table.columns |> List.tryFind(fun col ->  match col with
                                                                                            | IntColumn i when i.name = c -> true
                                                                                            | VarColumn v when v.name = c -> true
                                                                                            | _ -> false)
                                                 match column with
                                                    | Some col -> (col, d)
                                                    | None -> failwithf "no column named %s exists on table %s" c table.name )

It is great in F# how we can let the types guide us. If you look at the signature of the function above then we can see that it is:

getColumnsByNames (columnNames: (string * SortDirection) list) -> (table:Table) -> (Column * SortDirection) list

When you look at the types you can see that there are not too many ways this function could be implemented. Using what is in the room as Erik Meijer would say we go through the columns on the table and match them up with the column names that were passed in (throwing an exception if a name is passed in that is not on the table) and then return the actual column along with the sort direction.

F# is proving to be an interesting choice in writing the database comparison library. It is a totally different way of thinking but I feel that I’m starting to come to terms with thinking functionally.

If you want to check out the full source code and delve deeper feel free to check out the SqlJuxt GitHub repository.

SqlJuxt – Using disposable in F# to drop a test database

The integration tests in SqlJuxt need to do the following:

  • Create two databases
  • Set the databases up in a certain state (create tables, views etc)
  • Compare them
  • Assert the result of the comparison
  • Clean up the databases at the end (drop them)

Before I dive in to how I went about making this work I think its good to take a look at how the finished test looks:

[<Fact>]
let ``should return identical when two tables are the same``() =
    use left = createDatabase()
    use right = createDatabase()
     
    let table = CreateTable "TestTable"
                    |> WithNullableInt "Column1"
                    |> Build 

    runScript left table
    runScript right table
        
    loadSchema left.ConnectionString
            |> compareWith right.ConnectionString
            |> should equal IsMatch

I think that test reads really well. In fact you can tell exactly what is going on in the test from the code which is one of the key ingredients of a good test. The test is creating two databases, then creating the same table on both of the databases. It then compares them using the SqlJuxt library and expects the databases to match. The result of the comparison is a discriminate union which I will talk about more in an upcoming post. For now you can read that it says “should equal IsMatch” which is really clear.

The astute reader will notice that nowhere in the test does it mention dropping the databases so you might wonder how this is done. The secret behind this is IDisposable. I got the idea from reading this page on let, use and do on the F# for fun and profit site. Scott talks about using the dispose to stop a timer so I thought it would be neat to use it to drop the database.

To make this work the createDatabase function returns a class that implements IDisposable. Notice that the variables left and right are declared using the ‘use’ keyword and not the ‘let’ keyword. This means that when the variables go out of scope Dispose is automatically called.

This is how the disposable database type is defined:

type DisposableDatabase(name, connectionString) =

    member this.ConnectionString = connectionString
    member this.Name = name

    interface System.IDisposable with 
        member this.Dispose() = 
            dropDatabase this.Name

The code is a little bit clunky as we have to declare a class to implement IDisposable but the cool part is that we do not have to explicitly drop the database in our test it just happens for us.

If you want to check out the full source code and delve deeper feel free to check out the SqlJuxt GitHub repository.