test: add ExpectedInstalledName function

The ExpectedInstalledName function returns the expected full name of a
plugin binary after it's installed.

This is used for tests that need to copy the binary to some place before
they can run commands and ensure the logic for managing plugins conforms
to the docs/specs.

test/plugin_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"github.com/hashicorp/go-version"
+	"github.com/hashicorp/packer-plugin-sdk/plugin"
 )
 
 var compiledPlugins = struct {
@@ -83,6 +84,23 @@ func BinaryName(version *version.Version) string {
 	return retStr
 }
 
+// ExpectedInstalledName is the expected full name of the plugin once installed.
+func ExpectedInstalledName(versionStr string) string {
+	v := version.Must(version.NewSemver(versionStr))
+
+	ext := ""
+	if runtime.GOOS == "windows" {
+		ext = ".exe"
+	}
+
+	return fmt.Sprintf("packer-plugin-tester_v%s%s_x%s.%s_%s_%s%s",
+		v.Core().String(),
+		v.Prerelease(),
+		plugin.APIVersionMajor,
+		plugin.APIVersionMinor,
+		runtime.GOOS, runtime.GOARCH, ext)
+}
+
 // BuildSimplePlugin creates a plugin that essentially does nothing.
 //
 // The plugin's code is contained in a subdirectory of this, and lets us