feat: std.TestSetPrevRealm (gnolang#891)

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# Description

Thanks to @albttx, we now have `std.PrevRealm` gnolang#667

However it seems like doesn't work on testcase(that can be run by `gno
test` command) as what we expected.
> `gno test` uses its own Context which makes few other functions (like
GetRealmPath) doesn't work neither.

So I made little helper very similar to `std.TestSetOrigCaller`

---
## Discussion Need
`std.TestSetOrigCaller` takes single parameter and two different type
can be passed
1. If `std.Address` type is passed, -> TestSetPrevRealm will take it as
user address => return user address not realm.
2. If `string` type is passed, -> TestSetPrevRealm will take it as
pkg_path => return pkg address(using bech32) and pkg_path
> Since string parameter is being used without any verification in this
pr, How about reusing verification logic from here
??https://github.com/gnolang/gno/blob/408fc68d4b3c189dbc6a608c590a86c661ae232a/tm2/pkg/std/memfile.go#L33-L68


## Contributors Checklist

- [x] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests

## Maintainers Checklist

- [x] Checked that the author followed the guidelines in
`CONTRIBUTING.md`
- [x] Checked the conventional-commit (especially PR title and verb,
presence of `BREAKING CHANGE:` in the body)
- [x] Ensured that this PR is not a significant change or confirmed that
the review/consideration process was appropriate for the change

examples/gno.land/r/x/test_prev/gno.mod

@@ -0,0 +1,8 @@
+module gno.land/r/x/test_prev
+
+require (
+	gno.land/p/demo/grc/grc20 v0.0.0-latest
+	gno.land/p/demo/ufmt v0.0.0-latest
+	gno.land/p/demo/users v0.0.0-latest
+	gno.land/r/demo/users v0.0.0-latest
+)

examples/gno.land/r/x/test_prev/test_prev.gno

@@ -0,0 +1,18 @@
+package test_prev
+
+import (
+	"std"
+
+	pusers "gno.land/p/demo/users"
+	"gno.land/r/demo/foo20"
+)
+
+func DoSomeWithUserBalance() string {
+	caller := std.GetOrigCaller()
+	balance := foo20.BalanceOf(pusers.AddressOrName(caller))
+
+	if balance > 100 {
+		return "rich user"
+	}
+	return "poor user"
+}

examples/gno.land/r/x/test_prev/test_prev_test.gno

@@ -0,0 +1,32 @@
+package test_prev
+
+import (
+	"std"
+	"testing"
+
+	"gno.land/r/demo/foo20"
+)
+
+func TestDoSomeWithUserBalancePoor(t *testing.T) {
+	std.TestSetOrigCaller("g1jg8mtutu9khhfwc4nxmuhcpftf0pajdhfvsqf5")
+	if DoSomeWithUserBalance() != "poor user" {
+		t.Error("expected poor user")
+	}
+}
+
+func TestDoSomeWithUserBalanceRichButPoor(t *testing.T) {
+	std.TestSetOrigCaller("g1jg8mtutu9khhfwc4nxmuhcpftf0pajdhfvsqf5")
+	foo20.Faucet() // foo20 will mint tokens to this realm(std.PrevRealm) not user
+	if DoSomeWithUserBalance() != "poor user" {
+		t.Error("expected poor user")
+	}
+}
+
+func TestDoSomeWithUserBalanceRich(t *testing.T) {
+	std.TestSetPrevAddr("g1jg8mtutu9khhfwc4nxmuhcpftf0pajdhfvsqf5")
+
+	foo20.Faucet() // foo20 will mint tokens to this realm not user
+	if DoSomeWithUserBalance() != "rich user" {
+		t.Error("expected rich user")
+	}
+}

gnovm/tests/stdlibs/std/std.gno

@@ -8,6 +8,8 @@ func ClearStoreCache()            // injected
 
 func TestSetOrigCaller(addr Address)  { testSetOrigCaller(string(addr)) }
 func TestSetOrigPkgAddr(addr Address) { testSetOrigPkgAddr(string(addr)) }
+func TestSetPrevRealm(pkgPath string) { testSetPrevRealm(pkgPath) }
+func TestSetPrevAddr(addr Address)    { testSetPrevAddr(string(addr)) }
 func TestSetOrigSend(sent, spent Coins) {
 	sentDenom, sentAmt := sent.expandNative()
 	spentDenom, spentAmt := spent.expandNative()
@@ -24,6 +26,8 @@ func callerAt(n int) string
 // native bindings
 func testSetOrigCaller(s string)
 func testSetOrigPkgAddr(s string)
+func testSetPrevRealm(s string)
+func testSetPrevAddr(s string)
 func testSetOrigSend(
 	sentDenom []string, sentAmt []int64,
 	spentDenom []string, spentAmt []int64)

gnovm/tests/stdlibs/std/std.go

@@ -5,6 +5,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/gnolang/gno/gnovm/stdlibs"
+
 	gno "github.com/gnolang/gno/gnovm/pkg/gnolang"
 	"github.com/gnolang/gno/gnovm/stdlibs/std"
 	"github.com/gnolang/gno/tm2/pkg/crypto"
@@ -100,6 +102,21 @@ func X_testSetOrigPkgAddr(m *gno.Machine, addr string) {
 	m.Context = ctx
 }
 
+func X_testSetPrevRealm(m *gno.Machine, pkgPath string) {
+	m.Frames[m.NumFrames()-2].LastPackage = &gno.PackageValue{PkgPath: pkgPath}
+}
+
+func X_testSetPrevAddr(m *gno.Machine, addr string) {
+	// clear all frames to return mocked origin caller
+	for i := m.NumFrames() - 1; i > 0; i-- {
+		m.Frames[i].LastPackage = nil
+	}
+
+	ctx := m.Context.(stdlibs.ExecContext)
+	ctx.OrigCaller = crypto.Bech32Address(addr)
+	m.Context = ctx
+}
+
 func X_testSetOrigSend(m *gno.Machine,
 	sentDenom []string, sentAmt []int64,
 	spentDenom []string, spentAmt []int64,