test(sdk): make the plugin spec dir customizable

Author: EtienneM

.gitignore

@@ -22,3 +22,5 @@ _testmain.go
 *.exe
 *.test
 *.prof
+
+_dev/plugins

README.md

@@ -12,7 +12,21 @@ A collection of helper packages to extend Docker Engine in Go
 
 See the [understand Docker plugins documentation section](https://docs.docker.com/engine/extend/plugins/).
 
-### Release a New Version
+## Test Environment
+
+It is possible to execute the tests in a Docker environment by running:
+
+```shell
+make test
+```
+
+In a non-Docker environment, you may want to define the environment variable `PLUGIN_SPEC_DIR` to a user-writable folder such as:
+
+```shell
+PLUGIN_SPEC_DIR=$(pwd)/_dev go test -v ./...
+```
+
+## Release a New Version
 
 Bump new version number in:
 

_dev/.gitkeep

@@ -39,7 +39,11 @@ func createPluginSpecDirWindows(name, address, daemonRoot string) (string, error
 }
 
 func createPluginSpecDirUnix(name, address string) (string, error) {
-	pluginSpecDir := PluginSpecDir("/etc/docker")
+	myPluginSpecDir := os.Getenv("PLUGIN_SPEC_DIR")
+	if myPluginSpecDir == "" {
+		myPluginSpecDir = "/etc/docker"
+	}
+	pluginSpecDir := PluginSpecDir(myPluginSpecDir)
 	if err := os.MkdirAll(pluginSpecDir, 0755); err != nil {
 		return "", err
 	}