Ruthlessly Helpful

Stephen Ritchie's offerings of ruthlessly helpful .NET practices.

Monthly Archives: January 2012

Four Ways to Fake Time, Part 2

In Part 1 of this four part series you learned how a code’s implicit dependency on the system clock can make the software difficult to test. The first post presented a very simple solution, pass in the clock as a method parameter. It is effective, however, adding a new parameter to every method of a class isn’t always the best solution.

Fake Time 2: Brute Force Property Injection

Here is a second way to fake time. It is brute force in the sense that it is rudimentary. Using full-blown dependency injection with an IoC container is left as an exercise for the reader. The goal of this post is to illustrate the principle and provide you with a technique you can use today.

Perhaps an example would be helpful …

using System;
using Lender.Slos.Utilities.Configuration;

namespace Lender.Slos.Financial
{
    public class ModificationWindow
    {
        private readonly IModificationWindowSettings _settings;

        public ModificationWindow(
            IModificationWindowSettings settings)
        {
            _settings = settings;
        }

        // This property is for testing use only
        private DateTime? _now;
        public DateTime Now
        {
            get { return _now ?? DateTime.Now; }
            internal set { _now = value; }
        }

        public bool Allowed()
        {
            var now = this.Now;

            // Start date's month & day come from settings
            var startDate = new DateTime(
                now.Year,
                _settings.StartMonth,
                _settings.StartDay);

            // End date is 1 month after the start date
            var endDate = startDate.AddMonths(1);

            if (now >= startDate &&
                now < endDate)
            {
                return true;
            }

            return false;
        }
    }
}

In this example code, the Allowed method changed very little from how it was written at the end of the first post. The primary difference is that there isn’t any clock optional argument. The value of the now variable comes from the new class property named Now.

Let’s take a closer look at the Now property. First, it has a backing variable named _now, which is declared as a nullable DateTime. Second, since _now defaults to null, this means that the Now property getter will return System.DateTime.Now if the property is never set. In other words, if the Now property is never set then that property behaves like a call to System.DateTime.Now.

Note that the null coalescing operator (??) expression in the getter can be rewritten as follows:

get
{
    return _now == null ? DateTime.Now : _now.Value;
}

And so, if our test code sets the Now property to a specific DateTime value then that property returns that DateTime value, instead of System.DateTime.Now. This allows the test code to “freeze the clock” before calling the method-under-test.

The following is the revised test method. It sets the Now property to the currentTime value at the end of the arrangement section. This, in effect, fakes the Allowed method, and establishes a known value for the clock.

[TestCase(1)]
[TestCase(5)]
[TestCase(12)]
public void Allowed_WhenCurrentDateIsInsideModificationWindow_ExpectTrue(
    int startMonth)
{
    // Arrange
    var settings = new Mock<IModificationWindowSettings>();
    settings
        .SetupGet(e => e.StartMonth)
        .Returns(startMonth);
    settings
        .SetupGet(e => e.StartDay)
        .Returns(1);

    var currentTime = new DateTime(
        DateTime.Now.Year,
        startMonth,
        13);

    var classUnderTest = new ModificationWindow(settings.Object);

    classUnderTest.Now = currentTime; // Set the value of Now; freeze the clock

    // Act
    var result = classUnderTest.Allowed();

    // Assert
    Assert.AreEqual(true, result);
}

There is one more subtlety to mention. The test method cannot set the class-under-test’s Now property without being allowed access. This is accomplished by adding the following line to the end of the AssemblyInfo.cs file in the Lender.Slos.Financial project, which declares the class-under-test.

[assembly: InternalsVisibleTo("Tests.Unit.Lender.Slos.Financial")]

The use of InternalsVisibleTo establishes a friend assembly relationship.

Pros:

  1. A straightforward, KISS approach
  2. Can work with .NET Framework 2.0
  3. No impact on class-users and method-callers
  4. Isolated change, minimal risk
  5. Testability is greatly improved

Cons:

  1. Improves testability only one class at a time
  2. Adds a testing-use-only property to the class

I use this approach when working with legacy or Brownfield code. It is a minimally invasive technique.

In the next part of this Fake Time series we’ll look at the IClock interface and a constructor injection approach.

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Four Ways to Fake Time

Are your unit tests failing because the code-under-test is coupled to the system clock? In other words, does the method you are testing use the System.DateTime.Now property, and that dependency is making it hard to properly unit test the code?

Calendar

This series of posts presents four ways to fake time as a means of improving testability. Specifically, we’ll look at these four techniques:

  1. The Optional ‘clock’ Parameter
  2. Brute Force Property Injection
  3. Inject The IClock Interface
  4. Mock Isolation Framework

Time Is Bumming Me Out

Time is so rigid. It keeps on ticking, ticking … into the future. The code becomes dependent on the system clock. That dependency makes it hard to properly test the code. Worse, the test code cannot find a lurking bug … until *boom* … the bug blows the system up.

Perhaps an example would be helpful …

public bool Allowed()
{
    // Start date's month & day come from settings
    var startDate = new DateTime(
        DateTime.Now.Year,
        _settings.StartMonth,
        _settings.StartDay);

    // End date is 1 month after the start date
    var endDate = new DateTime(
        DateTime.Now.Year,
        _settings.StartMonth + 1, // This is the lurking bug!
        _settings.StartMonth);

    if (DateTime.Now >= startDate &&
        DateTime.Now < endDate)
    {
        return true;
    }

    return false;
}

Notice the lurking bug in this code? Well, if the start month is December then a defect emerges at runtime. The error message you would see looks something like this:

System.ArgumentOutOfRangeException : Year, Month, and Day parameters describe an un-representable DateTime.

This defect is not too hard to notice, if you envision the value in the _settings.StartMonth property is 12. However, the problem with lurking bugs, they go unnoticed until … bang! At some future date (all too often in production) the software hiccups.

In the following code sample, the defect will be found when the continuous integration server runs the tests in December. This is a fairly typical unit testing approach, intended to test the Allowed method.

[Test]
public void Allowed_WhenCurrentDateIsOutsideModificationWindow_ExpectFalse()
{
    // Arrange
    var startMonth = DateTime.Now.Month;

    var settings = new Mock<IModificationWindowSettings>();
    settings
        .SetupGet(e => e.StartMonth)
        .Returns(startMonth + 1);
    settings
        .SetupGet(e => e.StartDay)
        .Returns(1);

    var classUnderTest = new ModificationWindow(settings.Object);

    // Act
    var result = classUnderTest.Allowed();

    // Assert
    Assert.AreEqual(false, result);
}

You don’t want to go into work on 1-Dec and find that this test is suddenly failing. The test method fails in December because that’s when startMonth is 12 and the defect is revealed. You’ll have a sickening thought, “Wait a second … is it failing in production?”

The production code is not working as intended, and worse than that, the test code never found the issue before the defect went into production.

If you revise the test code to include a few test cases, like the ones shown below, then the boundary conditions are covered and the defect is found every time these test cases are run. However, this test method has another flaw. It cannot pass for all three cases because the code-under-test has a dependency on DateTime.Now.

[TestCase(1)]
[TestCase(5)]
[TestCase(12)]
public void Allowed_WhenCurrentDateIsOutsideModificationWindow_ExpectFalse(
    int startMonth)
{
    // Arrange
    var settings = new Mock<IModificationWindowSettings>();
    settings
        .SetupGet(e => e.StartMonth)
        .Returns(startMonth + 1);
    settings
        .SetupGet(e => e.StartDay)
        .Returns(1);

    var classUnderTest = new ModificationWindow(settings.Object);

    // Act
    var result = classUnderTest.Allowed();

    // Assert
    Assert.AreEqual(false, result);
}

Before we investigate any further, let’s go back and revise the code-under-test to fix the bug. Here is an improved implementation of the Allowed method.

public bool Allowed()
{
    // Start date's month & day come from settings
    var startDate = new DateTime(
        DateTime.Now.Year,
        _settings.StartMonth,
        _settings.StartDay);

    // End date is 1 month after the start date
    var endDate = startDate.AddMonths(1);

    if (DateTime.Now >= startDate &&
        DateTime.Now < endDate)
    {
        return true;
    }

    return false;
}

Imagine that today is Friday the 13th of January 2012. When we run the test cases the first case passes, but the other two fail. We want all three test cases to pass every time they are run.

Fake Time 1: The Optional ‘Clock’ Parameter

Let’s change the code-under-test so that time is provided as an optional parameter. This approach is made possible by .NET Framework 4.0, which allows C# developers to define optional parameters.

public bool Allowed(DateTime? clock)
{
    var now = clock ?? DateTime.Now; // If no clock is provided then use Now.

    // Start date's month & day come from settings
    var startDate = new DateTime(
        now.Year,
        _settings.StartMonth,
        _settings.StartDay);

    // End date is 1 month after the start date
    var endDate = startDate.AddMonths(1);

    if (now >= startDate &&
        now < endDate)
    {
        return true;
    }

    return false;
}

Now that the code-under-test accepts this ‘clock’ parameter, the test method is modified, as follows. All three test cases now pass.

[TestCase(1)]
[TestCase(5)]
[TestCase(12)]
public void Allowed_WhenCurrentDateIsInsideModificationWindow_ExpectTrue(
    int startMonth)
{
    // Arrange
    var settings = new Mock<IModificationWindowSettings>();
    settings
        .SetupGet(e => e.StartMonth)
        .Returns(startMonth);
    settings
        .SetupGet(e => e.StartDay)
        .Returns(1);

    var currentTime = new DateTime(
        DateTime.Now.Year,
        startMonth,
        13);

    var classUnderTest = new ModificationWindow(settings.Object);

    // Act
    var result = classUnderTest.Allowed(currentTime);

    // Assert
    Assert.AreEqual(true, result);
}

Pros:

  1. The simplest thing that could possibly work; a KISS approach
  2. Minimal impact to method callers
  3. Isolated changes, lower risk
  4. Testability is greatly improved

Cons:

  1. Only works with .NET Framework 4
  2. Method callers are able to pass improper dates and times, invalidating the method’s expected behavior
  3. Improves testability only one method at a time
  4. Adds testing-use-only parameters to method signatures

I recommend this approach when working with legacy or Brownfield code, which has been brought up to .NET 4, and a minimally invasive, very isolated technique is indicated.

In the next part of this Fake Time series we’ll look at a brute force, property injection approach.

Crossderry Interview

Earlier in the month, Crossderry interviewed me about my book Pro .NET Best Practices. Below is the entire four-part interview. Reprinted with the permission of @crossderry.

Project Mgmt and Software Dev Best Practice

Q: Your book’s title notwithstanding, you’re keen to move people away from the term “best practices.” What is wrong with “best practices”?

A: My technical reviewer, Paul Apostolescu, asked me the same question. Paul often prompted me to really think things through.

I routinely avoid superlatives, like “best”, when dealing with programmers, engineers, and other left-brain dominant people. Far too often, a word like that becomes a huge diversion with heated discussions centering on the topic of what is the singularly best practice. It’s like that old saying, the enemy of the good is the best. Too much time is wasted searching for the best practice when there is clearly a better practice right in front of you.

A “ruthlessly helpful” practice is my pragmatist’s way of saying, let’s pick a new or different practice today because we know it pays dividends. Over time, iteratively and incrementally, that incumbent practice can be replaced by a better practice, until then the team and organization reaps the rewards.

As for the title of book, I originally named it “Ruthlessly Helpful .NET”. The book became part of an Apress professional series, and the title “Pro .NET Best Practices” fits in with a prospective reader and booksellers’ expectations for books in that series.

Why PM Matters to Developers

Here we focus on why he spent so much time on PM-relevant topics:

Q: One of the pleasant surprises in the book was the early attention you paid to strategy, value, scope, deliverables and other project management touchstones. Why so much PM?

A: I find that adopting a new and different practice — in the hope that it’ll be ruthlessly helpful one — is an initiative, kinda like a micro-project. This can happen at so many levels … an individual developer, a technical leader, the project manager, the organization.

For the PM and for the organization, they’re usually aware that adopting a set of better practices is a project to be managed. For the individual or group, that awareness is often missing and the PM fundamentals are not applied to the task. I felt that my book needed to bring in the relevant first-principles of project management to raise some awareness and guide readers toward the concepts that make these initiatives more successful.

Ruthlessly Helpful Project Management

We turn to the project manager’s role:

Q: Can you give an example or three of how project managers can be “ruthlessly helpful” to their development teams?

A: Here are a few:

1) Insist that programmers, engineers and other technical folks go to the whiteboard. Have them draw out and diagram their thinking. ”‘Can you draw it up for everyone to see?” Force them to share their mental image and understanding. You will find that others were making bad assumptions and inferences. Never assume that your development team is on the same page without literally forcing them to be on the same page.

2) Verify that every member of our development team is 100% confident that their component or module works as they’ve intended it to work. I call this: “Never trust an engineer who hesitates to cross his own bridge.” Many developer’s are building bridges they never intend to cross. I worked on fixed-asset accounting software, but I was never an accountant. The ruthlessly helpful PM asks the developer to demonstrate their work by asking things like “… let me see it in action, give it a quick spin, show me how you’re doing on this feature …”. These are all friendly ways to ask a developer to show you that they’re willing to cross their own bridge.

3) Don’t be surprised to find that your technical people are holding back on you. They’re waiting until there are no defects in their work. Perfectionists wish that their blind spots, omissions, and hidden weakness didn’t exist. Here’s the dilemma; they have no means to find the defects that are hidden to them. The cure they pick for this dilemma is to keep stalling until they can add every imaginable new feature and uncover any defect. The ruthlessly helpful PM knows how to find effective ways to provide the developers with dispassionate, timely, and non-judgmental feedback so they can achieve the desired results.

Common Obstacles PMs Introduce

This question — about problems project managers impose on their projects — wraps up my interview with Stephen Ritchie.

Q: What are common obstacles that project managers introduce into projects?

A: Haste. I like to say, “schedule pressure is the enemy of good design.” During project retrospectives, all too often, I find the primary technical design driver was haste. Not maintainability, not extensibility, not correctness, not performance … haste. This common obstacle is a silent killer. It is the Sword of Damocles that … when push comes to shove … drives so many important design objectives underground or out the window.

Ironically, the haste is driven by an imagined or arbitrary deadline. I like to remind project managers and developers that for quick and dirty solutions … the dirty remains long after the quick is forgotten. At critical moments, haste is important. But haste is an obstacle when it manifests itself as technical debt, incurred carelessly and having no useful purpose.

Other obstacles include compartmentalization, isolation, competitiveness, and demotivation. Here’s the thing. Most project managers need to get their team members to bring creativity, persistence, imagination, dedication, and collaboration to their projects if the project is going to be successful. These are the very things team members *voluntarily* bring to the project.

Look around the project; anything that doesn’t help and motivate individuals to interact effectively is an obstacle. Project managers must avoid introducing these obstacles and focus on clearing them.

[HT @crossderry Thank you for the interview and permission to reprint it on my blog.]

The Prime Directive

When creating test cases, I find that using prime numbers helps avoid coincidental arithmetic issues and helps make debugging easier.

A common coincidental arithmetic problem occurs when a test uses the number 2. These three expressions: 2 + 2, 2 * 2, and System.Math.Pow(2, 2) are all equal to 4. When using the number 2 as a test value, there are many ways the test falsely passes. Arithmetic errors are less likely to yield an improper result when the test values are different prime numbers.

Consider a loan that has a principal of $12,000.00, a term of 360 payments, an annual interest rate of 12%, and, of course, don’t forget that there are 12 months in a year. Because the coincidental factor is 12 in all these numbers, this data scenario is a very poor choice as a test case.

In this code listing, the data-driven test cases use prime numbers and prime-derived variations to create uniqueness.

[TestCase(7499, 1.79, 0, 72.16)]
[TestCase(7499, 1.79, -1, 72.16)]
[TestCase(7499, 1.79, -73, 72.16)]
[TestCase(7499, 1.79, int.MinValue, 72.16)]
[TestCase(7499, 1.79, 361, 72.16)]
[TestCase(7499, 1.79, 2039, 72.16)]
[TestCase(7499, 1.79, int.MaxValue, 72.16)]
public void ComputePayment_WithInvalidTermInMonths_ExpectArgumentOutOfRangeException(
    decimal principal,
    decimal annualPercentageRate,
    int termInMonths,
    decimal expectedPaymentPerPeriod)
{
    // Arrange
    var loan =
        new Loan
            {
                Principal = principal,
                AnnualPercentageRate = annualPercentageRate,
            };

    // Act
    TestDelegate act = () => loan.ComputePayment(termInMonths);

    // Assert
    Assert.Throws<ArgumentOutOfRangeException>(act);
}

Here’s a text file that lists the first 1000 prime numbers: http://primes.utm.edu/lists/small/1000.txt

Here’s a handy prime number next-lowest/next-highest calculator: http://easycalculation.com/prime-number.php

Also, I find that it’s often helpful to avoid using arbitrary, hardcoded strings. When the content in the string is unimportant, I use Guid.NewGuid.ToString(), or I write a test helper method like TestHelper.BuidString() to create random, unique strings. This helps avoid same-string coincidences.