Revert "Values without a backing env var should not be expanded (#368)" (#371)

This reverts commit 911fc5a223.

cmd/backup/config_provider_test.go

@@ -1,68 +0,0 @@
-package main
-
-import (
-	"os"
-	"reflect"
-	"testing"
-)
-
-func TestSource(t *testing.T) {
-	tests := []struct {
-		name           string
-		input          string
-		expectError    bool
-		expectedOutput map[string]string
-	}{
-		{
-			"default",
-			"testdata/default.env",
-			false,
-			map[string]string{
-				"FOO": "bar",
-				"BAZ": "qux",
-			},
-		},
-		{
-			"not found",
-			"testdata/nope.env",
-			true,
-			nil,
-		},
-		{
-			"braces",
-			"testdata/braces.env",
-			false,
-			map[string]string{
-				"FOO": "qux",
-				"BAR": "xxx",
-				"BAZ": "",
-			},
-		},
-		{
-			"expansion",
-			"testdata/expansion.env",
-			false,
-			map[string]string{
-				"BAR": "xxx",
-				"FOO": "xxx",
-				"BAZ": "xxx",
-				"QUX": "yyy",
-			},
-		},
-	}
-
-	os.Setenv("QUX", "yyy")
-	defer os.Unsetenv("QUX")
-
-	for _, test := range tests {
-		t.Run(test.name, func(t *testing.T) {
-			result, err := source(test.input)
-			if (err != nil) != test.expectError {
-				t.Errorf("Unexpected error value %v", err)
-			}
-			if !reflect.DeepEqual(test.expectedOutput, result) {
-				t.Errorf("Expected %v, got %v", test.expectedOutput, result)
-			}
-		})
-	}
-}