command: Fix TestMetaBackend_configuredChangeCopy_multiToNoDefaultWithoutDefault

As part of integrating the new "remote" backend we relaxed the requirement
that a "default" workspace must exist in all backends and now skip
migrating empty workspace states to avoid creating unnecessary "default"
workspaces when switching between backends that require it and backends
that don't, such as when switching from the local backend (which always
has a "default" workspace) to Terraform Enterprise.

command/meta_backend_test.go

@@ -1279,9 +1279,9 @@ func TestMetaBackend_configuredChangeCopy_multiToNoDefaultWithoutDefault(t *test
 	}
 
 	sort.Strings(workspaces)
-	expected := []string{"default", "env2"}
+	expected := []string{"env2"} // default is skipped because it is absent in the source backend
 	if !reflect.DeepEqual(workspaces, expected) {
-		t.Fatalf("bad: %#v", workspaces)
+		t.Fatalf("wrong workspaces\ngot:  %#v\nwant: %#v", workspaces, expected)
 	}
 
 	{
@@ -1306,7 +1306,7 @@ func TestMetaBackend_configuredChangeCopy_multiToNoDefaultWithoutDefault(t *test
 		// Verify existing workspaces exist
 		envPath := filepath.Join(backendLocal.DefaultWorkspaceDir, "env2", backendLocal.DefaultStateFilename)
 		if _, err := os.Stat(envPath); err != nil {
-			t.Fatal("env should exist")
+			t.Fatalf("%s should exist, but does not", envPath)
 		}
 	}
 
@@ -1314,7 +1314,7 @@ func TestMetaBackend_configuredChangeCopy_multiToNoDefaultWithoutDefault(t *test
 		// Verify new workspaces exist
 		envPath := filepath.Join("envdir-new", "env2", backendLocal.DefaultStateFilename)
 		if _, err := os.Stat(envPath); err != nil {
-			t.Fatal("env should exist")
+			t.Fatalf("%s should exist, but does not", envPath)
 		}
 	}
 }