Introduce Helmfile's own filesystem abstraction to correctly unit test some components (#307)

Use abstracted FS

Signed-off-by: Arkaitz Jimenez <arkaitzj@gmail.com>

Signed-off-by: Arkaitz Jimenez <arkaitzj@gmail.com>

pkg/tmpl/context.go

@@ -1,12 +1,13 @@
 package tmpl
 
-import "io/fs"
+import (
+	"github.com/helmfile/helmfile/pkg/filesystem"
+)
 
 type Context struct {
 	preRender bool
 	basePath  string
-	readFile  func(string) ([]byte, error)
-	readDir   func(string) ([]fs.DirEntry, error)
+	fs        *filesystem.FileSystem
 }
 
 // SetBasePath sets the base path for the template
@@ -14,10 +15,6 @@ func (c *Context) SetBasePath(path string) {
 	c.basePath = path
 }
 
-func (c *Context) SetReadFile(f func(string) ([]byte, error)) {
-	c.readFile = f
-}
-
-func (c *Context) SetReadDir(f func(string) ([]fs.DirEntry, error)) {
-	c.readDir = f
+func (c *Context) SetFileSystem(fs *filesystem.FileSystem) {
+	c.fs = fs
 }