all: update tests to use 'go mod download all' to populate go.sum

In anticipation of CL 318629, 'go mod download' without arguments will
not update go.mod or go.sum. Before 1.16, 'go mod download' would adds
sums for .mod files but not .zip files (which people didn't usually
notice). Many folks found the behavior of adding sums for .zip files
to be annoying.

This change alters tests to run 'go mod download all' to populate
go.sum files. This is equivalent to 'go mod download' without
arguments before CL 318629.

For golang/go#45332

Change-Id: I387d514176f798ae8f17b0b056194196718f57f5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/318811
Trust: Jay Conrod <[email protected]>
Run-TryBot: Jay Conrod <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>

Author: Jay Conrod

go/packages/packagestest/modules.go

@@ -174,7 +174,7 @@ func (modules) Finalize(exported *Exported) error {
 	// stuff in cache. All the files created by Export should be recreated.
 	inv := gocommand.Invocation{
 		Verb:       "mod",
-		Args:       []string{"download"},
+		Args:       []string{"download", "all"},
 		Env:        exported.Config.Env,
 		BuildFlags: exported.Config.BuildFlags,
 		WorkingDir: exported.Config.Dir,

internal/imports/mod_test.go

@@ -709,7 +709,7 @@ func setup(t *testing.T, main, wd string) *modTest {
 		t.Fatalf("checking if go.mod exists: %v", err)
 	}
 	if err == nil {
-		if _, err := env.invokeGo(context.Background(), "mod", "download"); err != nil {
+		if _, err := env.invokeGo(context.Background(), "mod", "download", "all"); err != nil {
 			t.Fatal(err)
 		}
 	}