feat: add Getenv to OSEnv interface (#460)

Adds Getenv(key string) string to the OSEnv interface, along with
implementations in defaultOSEnv, TestOSEnv, and the mock.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: Daniel McIlvaney

internal/app/azldev/systeminterfaces.go

@@ -103,3 +103,7 @@ func (e *defaultOSEnv) Chdir(dir string) error {
 	//nolint:wrapcheck // We are intentionally a pass-through.
 	return os.Chdir(dir)
 }
+
+func (e *defaultOSEnv) Getenv(key string) string {
+	return os.Getenv(key)
+}

internal/global/opctx/interfaces.go

@@ -168,6 +168,8 @@ type OSEnv interface {
 	Getwd() (string, error)
 	// Change the process's current working directory.
 	Chdir(path string) error
+	// Retrieve the value of the environment variable named by the key.
+	Getenv(key string) string
 	// Checks if the current user is a member of the given group.
 	IsCurrentUserMemberOf(groupName string) (bool, error)
 	// Looks up the group ID for the given group name.

internal/global/opctx/opctx_test/opctx_mocks.go

@@ -7,15 +7,37 @@ package testctx
 // to control the environment without mutating the host environment.
 type TestOSEnv struct {
 	workingDir string
+	envVars    map[string]string
 }
 
 // Constructs a new [TestOSEnv] instance with the default working directory initialized to "/".
 func NewTestOSEnv() *TestOSEnv {
 	return &TestOSEnv{
 		workingDir: "/",
+		envVars:    make(map[string]string),
 	}
 }
 
+// SetEnv sets a test environment variable on the [TestOSEnv] instance.
+//
+// Note that [SetEnv] is not part of the [opctx.OSEnv] interface, so it is only
+// available when working with [TestOSEnv] directly. The intended usage pattern
+// in tests is:
+//
+//	env := NewTestOSEnv()
+//	env.SetEnv("KEY", "VALUE")
+//	ctx := NewCtx(
+//	    ctx,
+//	    WithOSEnv(env),
+//	)
+//
+// This allows tests to configure environment variables without mutating the
+// real host environment while still passing an [opctx.OSEnv]-compatible value
+// into [NewCtx] via [WithOSEnv].
+func (env *TestOSEnv) SetEnv(key, value string) {
+	env.envVars[key] = value
+}
+
 // Getwd implements the [opctx.OSEnv] interface.
 func (env *TestOSEnv) Getwd() (string, error) {
 	return env.workingDir, nil
@@ -40,3 +62,8 @@ func (env *TestOSEnv) LookupGroupID(groupName string) (gid int, err error) {
 	// For testing purposes, we can return a fixed group ID.
 	return testGroupID, nil
 }
+
+// Getenv implements the [opctx.OSEnv] interface.
+func (env *TestOSEnv) Getenv(key string) string {
+	return env.envVars[key]
+}