Add replace program utility

[VenelinMartinov]

This adds a ReplaceProgram utility to pulumitest which replaces the Pulumi program used by the test.

I've written this quite a few times now, so it seems like a good candidate as a utility - should be useful when testing updates.

[danielrbradley]

I really like where this is heading - to make working with inline YAML programs really easy. I think we could do with a little more design around the end-to-end process of testing YAML programs.

One assumption that's baked in right now is that we're always driving the test from a physical source directory. For YAML programs there's no real requirement for this. Perhaps we could introduce a new top-level test constructor for dealing with inline tests better? Something like this perhaps ...

  test := NewPulumiInlineTest(t, opttest.AttachProviderBinary("gcp", "../bin"))
  test.WritePulumiYaml(`
name: yaml_empty
runtime: yaml
outputs:
	output: "output"
`)
  test.InstallStack("my-stack")
  update := test.Up()
  t.Log(update.StdOut)

I expect the next step from here would be some additional utilities for YAML programs to be able to perform targeted updates.

  test := NewPulumiInlineTest(t, opttest.AttachProviderBinary("gcp", "../bin"))
  test.WritePulumiYaml(`
name: yaml_empty
runtime: yaml
outputs:
	output: "output"
`)
  test.Up()
  test.UpdatePulumiYaml(
    yaml.AddResource("my-resource", yaml.Resource{
      Type: "aws:s3:Bucket",
    })

A side question here: are there Go types available for the valid YAML constructs that we could leverage here instead of reverting to strings?

[danielrbradley]

I wonder if either instead of WritePulumiYaml, or in addition to it, we should use a method that allows us to interact with the existing file too. This could then be leveraged by a typed YAML helper if we want to later.

For example:

test.UpdatePulumiYaml(func(source string) string {
    return `
name: yaml_empty
runtime: yaml
outputs:
	output: "output"
`
})

Which then allows targeted updates:

test.UpdatePulumiYaml(func(source string) string {
    return strings.ReplaceAll(source, "toBeReplaced", "newValue")
})

[VenelinMartinov]

I think that's for individual tests to implement as needed - it's easy enough to add something like

func testProgram(params interface{}) {

jsonParam := params.ToJson()

program := fmt.Sprintf(`
resource:
  myRes:
    myParam: %s
`, jsonParams)
}

I don't think we need to add all the possible methods to the testing library but I've found I am using WritePulumiYaml quite extensively, so I think it'd be useful to add here.

[VenelinMartinov]

Discussed offline with @danielrbradley, I've added a ReadYaml utility and have removed the tab replacement in favour of an early error and a suggested program.

The tab replacement could be ugly with mixed spaces and tabs.

[danielrbradley]

Notes from sync review.

In a follow-up PR, we'll add a new NewInlinePulumiTest constructor which takes the pulumiYaml string instead of the source directory path.

[danielrbradley]

Looks good once the TestReadProgram is passing

[pulumi-bot]

This PR has been shipped in release v0.1.3.