Learn Go with Tests

Writing tests

Writing a test is just like writing a function, with a few rules

• It needs to be in a file with a name like xxx_test.go

• The test function must start with the word Test

• The test function takes one argument only t *testing.T

• In order to use the *testing.T type, you need to import "testing", like we did with fmt in the other file

func TestHello(t *testing.T) {
	t.Run("saying hello to people", func(t *testing.T) {
		got := Hello("Chris")
		want := "Hello, Chris"
		assertCorrectMessage(t, got, want)
	})
 
	t.Run("empty string defaults to 'world'", func(t *testing.T) {
		got := Hello("")
		want := "Hello, World"
		assertCorrectMessage(t, got, want)
	})
 
}
 
func assertCorrectMessage(t testing.TB, got, want string) {
	t.Helper()
	if got != want {
		t.Errorf("got %q want %q", got, want)
	}
}

In your Go code, t *testing.T is used within your test function TestHello and the helper function assertCorrectMessage for several reasons related to writing tests in Go:

1. Access to Testing Methods: t *testing.T is a pointer to Go’s testing framework’s T type, which provides methods for controlling test execution and logging. By passing t into your test functions, you gain access to methods such as t.Errorf, t.Fatalf, t.Run, and t.Helper.

2. Running Subtests: The t.Run method allows you to define subtests or table-driven tests within your test function. This approach makes your tests more organized and can be useful for testing different scenarios or inputs for the same function. Each call to t.Run can be considered as a separate test case within the broader test function.

3. Error Reporting and Logging: The methods on *testing.T like t.Errorf are used for reporting errors. When you call t.Errorf, it logs the error message and marks the test as failed but continues execution. This is useful for running multiple checks within a single test and getting a report on all failures.

4. Helper Function: The t.Helper method in your assertCorrectMessage function is used to mark that function as a test helper. When this method is called, the function is skipped when reporting where an error occurred, making the error output more readable. It tells the test framework that the actual place of interest is where the helper function was called, not inside the helper function itself.

5. Interface testing.TB: In your assertCorrectMessage function, you use testing.TB instead of *testing.T. The testing.TB is an interface that is implemented by both *testing.T and *testing.B (where B is for benchmarks). Using testing.TB makes your helper function more flexible because it can be used with both testing and benchmarking.

In summary, t *testing.T and testing.TB are essential for structuring your tests, running subtests, reporting errors, and making your test code more maintainable and flexible in Go.

For helper functions, it’s a good idea to accept a testing.TB which is an interface that *testing.T and *testing.B both satisfy, so you can call helper functions from a test, or a benchmark (don’t worry if words like “interface” mean nothing to you right now, it will be covered later).

t.Helper() is needed to tell the test suite that this method is a helper. By doing this when it fails the line number reported will be in our function call rather than inside our test helper. This will help other developers track down problems easier. If you still don’t understand, comment it out, make a test fail and observe the test output. Comments in Go are a great way to add additional information to your code, or in this case, a quick way to tell the compiler to ignore a line. You can comment out the t.Helper() code by adding two forward slashes // at the beginning of the line. You should see that line turn grey or change to another color than the rest of your code to indicate it’s now commented out.

Check chapter 1 here

Property Based Testing

examples in golang ⇒ can help you with test

Benchmarking

https://quii.gitbook.io/learn-go-with-tests/go-fundamentals/iteration#benchmarking

run with test ⇒ go test -bench=.

Go’s built-in testing toolkit features a coverage tool. Whilst striving for 100% coverage should not be your end goal, the coverage tool can help identify areas of your code not covered by tests. If you have been strict with TDD, it’s quite likely you’ll have close to 100% coverage anyway.

Try running

go test -cover

You should see

PASS

coverage: 100.0% of statements

Go does not let you use equality operators with slices. You could write a function to iterate over each got and want slice and check their values but for convenience sake, we can use reflect.DeepEqual which is useful for seeing if any two variables are the same.

In Go, slices cannot be compared directly using the equality operator (==). This is because slices are reference types in Go, and comparing them directly would compare the references (addresses in memory), not the content of the slices. To compare the contents of two slices, you need to iterate over the elements and compare them individually, or use a convenience function like reflect.DeepEqual from the reflect package.

Using reflect.DeepEqual

reflect.DeepEqual is a function that checks if two variables are deeply equal. It’s a part of the reflect package in Go, which provides run-time reflection, allowing you to inspect and manipulate objects at run time. reflect.DeepEqual is useful for comparing complex types like slices, maps, structs, etc., where a simple == comparison is not possible or sufficient.

Here’s an example of how you can use reflect.DeepEqual to compare two slices:

package main
 
import (
    "fmt"
    "reflect"
)
 
func main() {
    slice1 := []int{1, 2, 3}
    slice2 := []int{1, 2, 3}
    slice3 := []int{4, 5, 6}
 
    fmt.Println("slice1 == slice2:", reflect.DeepEqual(slice1, slice2)) // true
    fmt.Println("slice1 == slice3:", reflect.DeepEqual(slice1, slice3)) // false
}

In this example, reflect.DeepEqual is used to compare slice1 with slice2 and slice3. It returns true when comparing slice1 and slice2 because their contents are identical, and false when comparing slice1 and slice3 as their contents differ.

Writing Your Own Comparison Function

If you prefer not to use reflect.DeepEqual (for example, for performance reasons, as reflect.DeepEqual can be slower and more memory-intensive), you can write your own function to compare slices:

package main
 
import "fmt"
 
func slicesEqual(a, b []int) bool {
    if len(a) != len(b) {
        return false
    }
    for i := range a {
        if a[i] != b[i] {
            return false
        }
    }
    return true
}
 
func main() {
    slice1 := []int{1, 2, 3}
    slice2 := []int{1, 2, 3}
    slice3 := []int{4, 5, 6}
 
    fmt.Println("slice1 == slice2:", slicesEqual(slice1, slice2)) // true
    fmt.Println("slice1 == slice3:", slicesEqual(slice1, slice3)) // false
}

This slicesEqual function first checks if the slices have the same length. If not, it returns false. Then it iterates over the slices, comparing each element. If any elements are different, it returns false. If all elements are the same, it returns true.

Using reflect.DeepEqual is more convenient and less error-prone, especially for complex types or deeply nested data structures. However, for simple cases or when performance is a concern, a custom comparison function may be more efficient.

Table Driven Test in golang

Table-driven testing is a popular testing pattern in Go (Golang), particularly well-suited for scenarios where you want to run the same test logic across different inputs and expected outputs. This approach is efficient, readable, and makes it easy to add new test cases.

Concept

In table-driven testing, you define a table (slice) of test cases. Each test case in the table is a struct that includes the input data for the test and the expected result. You then iterate over this slice, running the same test logic for each case.

This approach is especially useful for:

• Reducing code duplication.
• Making it easier to add new test cases.
• Improving test readability and maintenance.

Example

Let’s consider an example where we want to test a function Add that adds two integers.

package main
 
import "testing"
 
// Add returns the sum of two integers
func Add(a, b int) int {
    return a + b
}
 
// TestAdd is a table-driven test for the Add function
func TestAdd(t *testing.T) {
    tests := []struct {
        name string
        a, b int
        want int
    }{
        {"add two positive numbers", 2, 3, 5},
        {"add positive and negative", 1, -1, 0},
        {"add two negative numbers", -1, -2, -3},
        // add more test cases here
    }
 
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got := Add(tt.a, tt.b)
            if got != tt.want {
                t.Errorf("Add(%d, %d) = %d; want %d", tt.a, tt.b, got, tt.want)
            }
        })
    }
}

Explanation

• Test Table: The tests slice contains multiple test cases. Each case is defined by a struct with fields for inputs (a and b), the expected output (want), and a name (name) for the test case.
• Iteration: The for _, tt := range tests loop iterates over each test case.
• Running the Test: Inside the loop, t.Run is used to execute a subtest for each case. This allows each test case to be run independently, and it provides clearer test output, showing which cases pass or fail.
• Assertions: The actual function call (Add(tt.a, tt.b)) and the assertion (if got != tt.want) are inside the loop. If the function’s output doesn’t match the expected output, an error is reported with t.Errorf.

By using table-driven tests, you can easily see the different scenarios being tested and add new test cases by simply adding new entries to the tests slice. This pattern makes your tests more organized and easier to extend and maintain.

Dependency Injection Mocking Concurrency Testing in Golang

https://quii.gitbook.io/learn-go-with-tests/go-fundamentals/dependency-injection https://quii.gitbook.io/learn-go-with-tests/go-fundamentals/mocking