How to Achieve Test Coverage for Code Separated from Tests in Go?

Testing Coverage for Code Separated from Tests

Despite the advantage of organizing test files separately for a cleaner codebase and limiting tests to public API interactions, it poses a challenge in obtaining coverage for the target package under test (in this case, api_client).

To address this issue, we can leverage the -coverpkg flag along with the package name when running tests:

go test -cover -coverpkg "api_client" "api_client_tests"

This command will run the tests with coverage enabled for the api_client package.

While separating test files from code files is permissible, it's important to note that it deviates from Go's standard approach. This means that package-private variables or functions will not be accessible by tests outside of the package, even if they are in separate directories.

To enforce black-box testing, where tests should only access public API methods, you can still keep tests in separate packages without physically moving the files. For example:

<code class="go">// api_client.go
package api_client

// Private variable not accessible outside package
var privateVar = 10

func PublicMethod() {}</code>

<code class="go">// api_client_test.go
package api_client_tests

import (
    "testing"

    "api_client" // Import api_client package
)

func TestPublicMethod(t *testing.T) {
    api_client.PublicMethod()
}</code>

In this example, the privateVar and Method function from api_client.go are inaccessible to the test file, ensuring that tests interact only via the public API.

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