refactor: extract setupAction into ActionReader (#986)

This change extracts the functionality of reading an `action.y(a)ml` or
creation of a `(Synthetic Action)` into its own type to enable better
unit testing / mocking of those IO operations.

This is done in preparation for the implementation of pre/post action
support in act.

Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

act/runner/action_test.go

@@ -0,0 +1,133 @@
+package runner
+
+import (
+	"io"
+	"io/fs"
+	"strings"
+	"testing"
+
+	"github.com/nektos/act/pkg/model"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+)
+
+type closerMock struct {
+	mock.Mock
+}
+
+func (m *closerMock) Close() error {
+	m.Called()
+	return nil
+}
+
+func TestActionReader(t *testing.T) {
+	yaml := strings.ReplaceAll(`
+name: 'name'
+runs:
+  using: 'node16'
+  main: 'main.js'
+`, "\t", "  ")
+
+	table := []struct {
+		name        string
+		step        *model.Step
+		filename    string
+		fileContent string
+		expected    *model.Action
+	}{
+		{
+			name:        "readActionYml",
+			step:        &model.Step{},
+			filename:    "action.yml",
+			fileContent: yaml,
+			expected: &model.Action{
+				Name: "name",
+				Runs: model.ActionRuns{
+					Using: "node16",
+					Main:  "main.js",
+				},
+			},
+		},
+		{
+			name:        "readActionYaml",
+			step:        &model.Step{},
+			filename:    "action.yaml",
+			fileContent: yaml,
+			expected: &model.Action{
+				Name: "name",
+				Runs: model.ActionRuns{
+					Using: "node16",
+					Main:  "main.js",
+				},
+			},
+		},
+		{
+			name:        "readDockerfile",
+			step:        &model.Step{},
+			filename:    "Dockerfile",
+			fileContent: "FROM ubuntu:20.04",
+			expected: &model.Action{
+				Name: "(Synthetic)",
+				Runs: model.ActionRuns{
+					Using: "docker",
+					Image: "Dockerfile",
+				},
+			},
+		},
+		{
+			name: "readWithArgs",
+			step: &model.Step{
+				With: map[string]string{
+					"args": "cmd",
+				},
+			},
+			expected: &model.Action{
+				Name: "(Synthetic)",
+				Inputs: map[string]model.Input{
+					"cwd": {
+						Description: "(Actual working directory)",
+						Required:    false,
+						Default:     "actionDir/actionPath",
+					},
+					"command": {
+						Description: "(Actual program)",
+						Required:    false,
+						Default:     "cmd",
+					},
+				},
+				Runs: model.ActionRuns{
+					Using: "node12",
+					Main:  "trampoline.js",
+				},
+			},
+		},
+	}
+
+	for _, tt := range table {
+		t.Run(tt.name, func(t *testing.T) {
+			closerMock := &closerMock{}
+
+			readFile := func(filename string) (io.Reader, io.Closer, error) {
+				if tt.filename != filename {
+					return nil, nil, fs.ErrNotExist
+				}
+
+				return strings.NewReader(tt.fileContent), closerMock, nil
+			}
+
+			writeFile := func(filename string, data []byte, perm fs.FileMode) error {
+				assert.Equal(t, "actionDir/actionPath/trampoline.js", filename)
+				assert.Equal(t, fs.FileMode(0400), perm)
+				return nil
+			}
+
+			closerMock.On("Close")
+
+			sc := &StepContext{}
+			action, err := sc.readAction(tt.step, "actionDir", "actionPath", readFile, writeFile)
+
+			assert.Nil(t, err)
+			assert.Equal(t, tt.expected, action)
+		})
+	}
+}