Working with Unit Tests<\/h2>\n\n\n\n
We\u2019ll use the xUnit test framework and JetBrains Annotations in the following examples. These are the libraries I typically use, but all examples apply to other libraries.<\/p>\n\n\n\n
Regardless of your style of testing, it\u2019s essential to maintain a consistent approach across tests. In the cross-section of tests and generative assistants, there are three factors to consider when constructing a test suite:<\/p>\n\n\n\n
- \n
- Always think about the \u201cwhy\u201d. Tests are not inherently valuable, and carelessly adding tests to hit a metric can lead to bloat and a long-term maintenance burden. <\/li>\n\n\n\n
- When writing tests, you should see a test fail before it succeeds. It may seem obvious that a test may pass, but it’s a good habit to form to avoid bugs. Seeing a failure is especially important when AI Assistant can generate assertion statements.<\/li>\n\n\n\n
- Test isolation increases the reliability of tests by reducing interdependency between each test.<\/li>\n<\/ol>\n\n\n\n
JetBrains AI Assistant can accelerate your test creation, but please be mindful of how and when you use it. I\u2019ll show you techniques to generate and maintain tests against a service carefully<\/em>. <\/p>\n\n\n\n
These techniques will help keep you engaged and focused rather than autocompleting your way to a suite of tests you don\u2019t understand.<\/p>\n\n\n\n
Let\u2019s first look at the class we\u2019ll be testing, a
PersonService<\/code> with several methods of varying complexity.<\/p>\n\n\n\nusing System.Text;\n\nnamespace GeneratedDataTests;\n\npublic record Person(string Name, int Age);\n\npublic class PersonService\n{\n public double AverageAge(List<Person> people)\n {\n return people.Average(p => p.Age);\n }\n\n public string? LongestName(List<Person> people)\n {\n return people\n .OrderByDescending(p => p.Name)\n .ThenByDescending(p => p.Name.Length)\n .Select(p => p.Name)\n .FirstOrDefault();\n }\n\n public string CreateCsv(List<Person> person)\n {\n var sb = new StringBuilder($\"{nameof(Person.Age)},{nameof(Person.Name)}\");\n foreach (var (name, age) in person)\n {\n sb.AppendLine($@\"\"\"{name}\"\",\"\"{age}\"\"\");\n }\n return sb.ToString();\n }\n\n public List<Person> ProcessCsv(string csv)\n {\n var lines = csv.Split(Environment.NewLine, StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);\n var people = new List<Person>();\n \/\/ skip header\n foreach (var line in lines.Skip(1))\n {\n var values = line.Split(',');\n if (values.Length == 2)\n {\n var name = values[0].Trim('\"');\n var age = int.Parse(values[1].Trim('\"'));\n people.Add(new Person(name, age));\n }\n }\n return people;\n }\n}\n<\/pre>\n\n\n\nYou may find similar services in your applications, with logic encapsulated within helper methods. Let\u2019s start by first testing the
AverageAge<\/code> method. In a test class, start by adding this boilerplate code.<\/p>\n\n\n\nusing JetBrains.Annotations;\n\nnamespace GeneratedDataTests;\n\n[TestSubject(typeof(PersonService))]\npublic class PersonServiceTests\n{\n private readonly PersonService sut = new();\n \n [Fact]\n public void Find_Average_Age()\n {\n \/\/ Arrange: a 6 entry list of Person with random odd and even\n \/\/ ages between 30 to 90 and Japanese names.\n \n \/\/ Act\n var actual = sut.AverageAge(people);\n \n \/\/ Assert\n Assert.Equal(0, actual);\n }\n}\n<\/pre>\n\n\n\nA few critical elements to mention about this boilerplate:<\/p>\n\n\n\n
- \n
- The Arrange<\/strong> portion of our test is an AI Assistant prompt that will generate our dataset.<\/li>\n\n\n\n
- The Act <\/strong>portion executes the method of
AverageAge<\/code> as expected.<\/li>\n\n\n\n- The Assert<\/strong> portion already contains an assertion that is intentionally incorrect.<\/li>\n<\/ol>\n\n\n\n
While AI Assistant could undoubtedly generate an entire test, we want to remain thoughtful about what we\u2019re creating.<\/p>\n\n\n\n
After the prompting comment, we can press Enter<\/strong> to see what JetBrains AI Assistant offers as a potential dataset.<\/p>\n\n\n\n
![\"Test](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-8.png\")
<\/figure>\n\n\n\nOur next step is to run the functioning test to see if it fails.<\/p>\n\n\n\n
![\"Unit](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-9.png\")
<\/figure>\n\n\n\nHere, we can see both a failure of the test and a simplification in our assertion. Let\u2019s update our test to account for the precision of our
double<\/code> value.<\/p>\n\n\n\n[Fact]\npublic void Find_Average_Age()\n{\n \/\/ Arrange: a 6 entry list of Person with random odd and even\n \/\/ ages between 30 to 90 and Japanese names.\n var people = new List<Person>\n {\n new Person(\"Yuki\", 35),\n new Person(\"Hiroshi\", 42),\n new Person(\"Akiko\", 51),\n new Person(\"Satoshi\", 66),\n new Person(\"Naomi\", 73),\n new Person(\"Kenji\", 88)\n };\n \n \/\/ Act\n var actual = sut.AverageAge(people);\n \n \/\/ Assert\n Assert.Equal(59.17, Math.Round(actual, 2));\n}\n<\/pre>\n\n\n\nRerunning the test shows we now have a passing test.<\/p>\n\n\n\n
![\"Unit](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-10.png\")
<\/figure>\n\n\n\nNow, let\u2019s write another test. Under the
Find_Average_Age<\/code> method, hit the Enter <\/strong>key again. You\u2019ll notice something surprising.<\/p>\n\n\n\n![\"JetBrains](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-11.png\")
<\/figure>\n\n\n\nJetBrains AI Assistant\u2019s code completion has already determined the next test. In this case, it\u2019s very similar to our original test. Accepting this code may be tempting if you’re in a rush, but it could also be a mistake. In this case, running the generated test leads to failure.<\/p>\n\n\n\n
![\"The](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-15.png\")
<\/figure>\n\n\n\nRemember, you\u2019re still an essential part of the test-writing process. AI Assistant only proposes a \u201cpossible\u201d solution, but you must consider the proposal critically. This test fails because AI Assistant could not account for the implementation of
LongestName<\/code>. After all, we did not provide the implementation within the context. Let\u2019s look at it again.<\/p>\n\n\n\npublic string? LongestName(List<Person> people)\n{\n return people\n .OrderByDescending(p => p.Name)\n .ThenByDescending(p => p.Name.Length)\n .Select(p => p.Name)\n .FirstOrDefault();\n}<\/pre>\n\n\n\nAs you notice, we sort names alphabetically from Z to A and then by length. Generating test data is good, but you should be wary of automatically generated assertions. That is why I recommend writing your assertions before generating test data. Slowing down gives you time to think about the goal and value of the test. Let\u2019s fix the assertion and move on to a more interesting test case scenario, parsing comma-separated value strings.<\/p>\n\n\n\n
Let\u2019s start with the boilerplate for a test similar to the previous ones.<\/p>\n\n\n\n
[Fact]\npublic void Parse_Csv()\n{\n \/\/ Arrange: a string CSV with a header row \"Name\",\"Age\". Quote all values like \"12\". 5 rows only.\n \n \/\/ Act\n var actual = sut.ProcessCsv(csv);\n\n \/\/ Assert\n Assert.Equal(0, actual.Count);\n}<\/pre>\n\n\n\nPressing Enter <\/strong>after the comment produces a string literal for our method.<\/p>\n\n\n\n
![\"JetBrains](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-14.png\")
<\/figure>\n\n\n\nYou may use the quick fixes provided by ReSharper to change the string to use newer C# 12 features, but for the purposes of this test, it\u2019s unnecessary.<\/p>\n\n\n\n
Running the test fails because our assertion checks for a value of 0. Let\u2019s change the assertion after a failed test run to the following.<\/p>\n\n\n\n
\/\/ Assert\nAssert.Equal(5, actual.Count);<\/pre>\n\n\n\n
Now we should have a passing test. Hooray!<\/p>\n\n\n\n
If you must assert the items in the collection parsed correctly, you can use AI Assistant to generate the assertions based on the test data.<\/p>\n\n\n\n
![\"More](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-13.png\")
<\/figure>\n\n\n\nThe added assertions can undoubtedly add to more accurate tests, but they are lengthy, and you should use them sparingly. A new test asserting the accuracy of parsing would be more beneficial. Use your judgment here regarding how to approach this in your test suite.<\/p>\n\n\n\n
More Test Data Scenarios<\/h2>\n\n\n\n
When working within complex data-driven systems, you\u2019ll likely represent data in multiple formats. Some standard formats that come to mind include JSON, XML, and SQL schema. The need to work with numerous formats is where the JetBrains AI Assistant can shine, cutting out the doldrums of creating meaningful data and converting between formats.<\/p>\n\n\n\n
In a new AI Assistant chat, let\u2019s use the
Person<\/code> type to generate a JSON object with a collection of items.<\/p>\n\n\n\nWe\u2019ll use the following prompt:<\/p>\n\n\n\n
\n
Given the following record type, generate a JSON object with a `results` field that contains a 2-entry collection of Person objects. <\/p>\n\n\n\n
```csharp public record Person(string Name, int Age);```<\/code><\/p>\n<\/blockquote>\n\n\n\nThe JetBrains AI Assistant generates a JSON object ready to use for our tests that you can now place in a raw-string literal or within a file.<\/p>\n\n\n\n
![\"JSON](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-16.png\")
<\/figure>\n\n\n\nWe can continue the chat session with the following prompt:<\/p>\n\n\n\n
\n
Give me the same JSON object but now as XML with all values as attributes on elements of Person<\/p>\n<\/blockquote>\n\n\n\n
Which results in the following XML file.<\/p>\n\n\n\n
![\"XML](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-17.png\")
<\/figure>\n\n\n\nFinally, let\u2019s create a SQL table to store valuable new information. Within the same chat session, we can add yet another prompt. Remember, not all SQL is created equal. When working with SQL, add a hint denoting the desired syntax.<\/p>\n\n\n\n
\n
Could you write a SQL Schema creation script for a Person table with an additional
Id<\/code> column that is an identity column? Make sure it is SQLite syntax.<\/p>\n<\/blockquote>\n\n\n\nThe resulting output is as you\u2019d expect.<\/p>\n\n\n\n
![\"SQLite](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-18.png\")
<\/figure>\n\n\n\nLet\u2019s go further and generate new test data for our new SQLite table, maybe from a galaxy far far away.<\/p>\n\n\n\n
\n
Could you generate 5 insert statements for the Person table where the names are Star Wars characters?<\/p>\n<\/blockquote>\n\n\n\n
![\"SQL](\"https:\/\/blog.jetbrains.com\/wp-content\/uploads\/2024\/01\/image-19.png\")
<\/figure>\n\n\n\nWow! That\u2019s great because less time spent typing out test data means more time playing with my Star Wars figures. I mean doing serious work.<\/p>\n\n\n\n
Conclusion<\/h2>\n\n\n\n
As you\u2019ve seen in this post, AI Assistant can speed up your existing workflows by removing some of the tedium around generating test data. You could<\/em> <\/em><\/strong>undoubtedly type all this yourself, but these are typically the boring parts of software development. The crucial parts are problem-solving and delivering reliable solutions to your users, and I think this post demonstrates that you can do just that with JetBrains AI Assistant. <\/p>\n\n\n\n
Combined with the two decades of expertise baked into JetBrains products like ReSharper and JetBrains Rider, we believe AI Assistants can be another step towards building better applications. Read more on the official website to learn more about JetBrains AI Assistant.<\/a><\/p>\n\n\n\n
We hope you enjoyed this post, and if you have any comments, questions, or suggestions, please feel free to leave a comment.<\/p>\n\n\n\n
- The Act <\/strong>portion executes the method of
- The Arrange<\/strong> portion of our test is an AI Assistant prompt that will generate our dataset.<\/li>\n\n\n\n