Add replace program utility (#94)

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.

pulumitest/pulumiYAML.go

@@ -0,0 +1,39 @@
+package pulumitest
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// WritePulumiYaml writes the contents of the program string to the Pulumi.yaml file in the current testing directory.
+// YAML does not allow tabs, so this function will error if the program contains tabs.
+func (a *PulumiTest) WritePulumiYaml(t PT, program string) {
+	t.Helper()
+
+	// find the line of the program that contains tabs
+	lines := strings.Split(program, "\n")
+	for i, line := range lines {
+		if strings.Contains(line, "\t") {
+			ptFatalF(t, "program contains tabs on line %d: %s\nTry replacing it with:\n%s", i+1, line, strings.ReplaceAll(program, "\t", "    "))
+		}
+	}
+
+	pulumiYamlPath := filepath.Join(a.CurrentStack().Workspace().WorkDir(), "Pulumi.yaml")
+	err := os.WriteFile(pulumiYamlPath, []byte(program), 0o600)
+	if err != nil {
+		ptFatalF(t, "failed to replace program %s", err)
+	}
+}
+
+// ReadPulumiYaml reads the contents of the Pulumi.yaml file in the current testing directory.
+func (a *PulumiTest) ReadPulumiYaml(t PT) string {
+	t.Helper()
+
+	pulumiYamlPath := filepath.Join(a.CurrentStack().Workspace().WorkDir(), "Pulumi.yaml")
+	program, err := os.ReadFile(pulumiYamlPath)
+	if err != nil {
+		ptFatalF(t, "failed to read program %s", err)
+	}
+	return string(program)
+}

pulumitest/pulumiYAML_test.go

@@ -0,0 +1,43 @@
+package pulumitest_test
+
+import (
+	"testing"
+
+	"github.com/pulumi/providertest/pulumitest"
+	"github.com/stretchr/testify/require"
+)
+
+func TestReplaceProgram(t *testing.T) {
+	t.Parallel()
+
+	test := pulumitest.NewPulumiTest(t, "testdata/yaml_empty")
+
+	test.WritePulumiYaml(t, `
+name: yaml_empty
+runtime: yaml
+outputs:
+    output: "output"`)
+
+	res := test.Up(t)
+
+	require.Equal(t, "output", res.Outputs["output"].Value)
+}
+
+func TestReadProgram(t *testing.T) {
+	t.Parallel()
+
+	test := pulumitest.NewPulumiTest(t, "testdata/yaml_empty")
+
+	program := `
+name: yaml_empty
+runtime: yaml
+outputs:
+    output: "output"`
+
+	test.WritePulumiYaml(t, program)
+
+	res := test.Up(t)
+	require.Equal(t, "output", res.Outputs["output"].Value)
+
+	require.Equal(t, program, test.ReadPulumiYaml(t))
+}