multi transaction support in _filetest.gno

[moul]

The goal is to discover an efficient format that enables chaining tests in a single file while preserving the state between calls, mimicking real transactions in real-life scenarios.

This approach would help overcome a limitation with the banker module and std.GetOrigSend. Currently, the context sets std.GetOrigSend, and the final transfer only occurs when the VM keeper completes the transaction. By finding a suitable format, we can address this limitation and create a more realistic testing environment.

Maybe something like this:

package main

var x int

func main() {
	x++
	println("foo", x)
}

func main2() {
	x++
    println("bar", x)
}

// Output:
// foo 1

// NewTX: main2
// Output:
// bar 2

[moul]

Proposal by @ajnavarro, to follow the standard ExampleXXX pattern like in go.

package main

var x int

func ExampleTX1() {
	x++
	println("foo", x)
	// Output:
	// foo 1
}

func ExampleTX2() {
	x++
	println("bar", x)
	// Output:
	// bar 2
}

In our case, we want to ensure that each _test.gno file runs from top to bottom, so the first func Example is tx1, the second is tx2, and so on.

We also need to make sure that we load all the *.gno files, including other _test.gno files, but we need to take care to reset the context of the runtime for each _test.gno file, so that we don't have to care about the order of tests based on filename.

Pseudocode could be:

for _, testFile := range pkg.TestFiles() {
	if !testFile.HasATestOrExampleFunc() { continue }
	m := machine.Load(pkg) // including the other test files

	// run test files without simulating various transactions.
	m.RunTestFuncs()
	// now, simulate one transaction per example
	m.Reset()
	for _, exampleFunc := range testFile.ExampleFuncs() {
		m.ResetContext()
		m.TXSequenceTimeHeight++
		m.Call(exampleFunc)
		m.SaveState()
	}
}