[MM-27919] Allow i18n and resources to be loaded using an environment variable (#15341)

* [MM-27919] Allow i18n and resources to be loaded using an environment variable

* Improve error message

* Modify environment variable name to be less ambiguous

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

testlib/resources.go

@@ -36,17 +36,26 @@ type testResourceDetails struct {
 	action  int8
 }
 
-// commonBaseSearchPaths is a custom version of what fileutils exposes. At some point, consolidate.
-var commonBaseSearchPaths = []string{
-	".",
-	"..",
-	"../..",
-	"../../..",
-	"../../../..",
+// getCommonBaseSearchPaths() is a custom version of what fileutils exposes. At some point, consolidate.
+func getCommonBaseSearchPaths() []string {
+	paths := []string{
+		".",
+		"..",
+		"../..",
+		"../../..",
+		"../../../..",
+	}
+
+	// this enables the server to be used in tests from a different repository
+	if mmPath := os.Getenv("MM_SERVER_PATH"); mmPath != "" {
+		paths = append(paths, mmPath)
+	}
+
+	return paths
 }
 
 func findFile(path string) string {
-	return fileutils.FindPath(path, commonBaseSearchPaths, func(fileInfo os.FileInfo) bool {
+	return fileutils.FindPath(path, getCommonBaseSearchPaths(), func(fileInfo os.FileInfo) bool {
 		return !fileInfo.IsDir()
 	})
 }
@@ -61,7 +70,7 @@ func findDir(dir string) (string, bool) {
 		return path.Dir(srcPath), true
 	}
 
-	found := fileutils.FindPath(dir, commonBaseSearchPaths, func(fileInfo os.FileInfo) bool {
+	found := fileutils.FindPath(dir, getCommonBaseSearchPaths(), func(fileInfo os.FileInfo) bool {
 		return fileInfo.IsDir()
 	})
 	if found == "" {