Write unit tests with the help of afero

Afero is a package that lets you mock out a filesystem with an in-memory filesystem.
It allows us to easily create the files required for a given test without worrying about
a cleanup step or different tests tripping on eachother when run in parallel.

Later on I'll standardise on using afero over the vanilla os package

pkg/commands/git_commands/worktree_loader_test.go

@@ -3,9 +3,195 @@ package git_commands
 import (
 	"testing"
 
+	"github.com/go-errors/errors"
+	"github.com/jesseduffield/lazygit/pkg/commands/models"
+	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
+	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
 )
 
+func TestGetWorktrees(t *testing.T) {
+	type scenario struct {
+		testName          string
+		repoPaths         *RepoPaths
+		before            func(runner *oscommands.FakeCmdObjRunner, fs afero.Fs)
+		expectedWorktrees []*models.Worktree
+		expectedErr       string
+	}
+
+	scenarios := []scenario{
+		{
+			testName: "Single worktree (main)",
+			repoPaths: &RepoPaths{
+				repoPath:     "/path/to/repo",
+				worktreePath: "/path/to/repo",
+			},
+			before: func(runner *oscommands.FakeCmdObjRunner, fs afero.Fs) {
+				runner.ExpectGitArgs([]string{"worktree", "list", "--porcelain"},
+					`worktree /path/to/repo
+HEAD d85cc9d281fa6ae1665c68365fc70e75e82a042d
+branch refs/heads/mybranch
+`,
+					nil)
+
+				_ = fs.MkdirAll("/path/to/repo/.git", 0o755)
+			},
+			expectedWorktrees: []*models.Worktree{
+				{
+					IsMain:        true,
+					IsCurrent:     true,
+					Path:          "/path/to/repo",
+					IsPathMissing: false,
+					GitDir:        "/path/to/repo/.git",
+					Branch:        "mybranch",
+					Name:          "repo",
+				},
+			},
+			expectedErr: "",
+		},
+		{
+			testName: "Multiple worktrees (main + linked)",
+			repoPaths: &RepoPaths{
+				repoPath:     "/path/to/repo",
+				worktreePath: "/path/to/repo",
+			},
+			before: func(runner *oscommands.FakeCmdObjRunner, fs afero.Fs) {
+				runner.ExpectGitArgs([]string{"worktree", "list", "--porcelain"},
+					`worktree /path/to/repo
+HEAD d85cc9d281fa6ae1665c68365fc70e75e82a042d
+branch refs/heads/mybranch
+
+worktree /path/to/repo-worktree
+HEAD 775955775e79b8f5b4c4b56f82fbf657e2d5e4de
+branch refs/heads/mybranch-worktree
+`,
+					nil)
+
+				_ = fs.MkdirAll("/path/to/repo/.git", 0o755)
+				_ = fs.MkdirAll("/path/to/repo-worktree", 0o755)
+				_ = fs.MkdirAll("/path/to/repo/.git/worktrees/repo-worktree", 0o755)
+				_ = afero.WriteFile(fs, "/path/to/repo-worktree/.git", []byte("gitdir: /path/to/repo/.git/worktrees/repo-worktree"), 0o755)
+			},
+			expectedWorktrees: []*models.Worktree{
+				{
+					IsMain:        true,
+					IsCurrent:     true,
+					Path:          "/path/to/repo",
+					IsPathMissing: false,
+					GitDir:        "/path/to/repo/.git",
+					Branch:        "mybranch",
+					Name:          "repo",
+				},
+				{
+					IsMain:        false,
+					IsCurrent:     false,
+					Path:          "/path/to/repo-worktree",
+					IsPathMissing: false,
+					GitDir:        "/path/to/repo/.git/worktrees/repo-worktree",
+					Branch:        "mybranch-worktree",
+					Name:          "repo-worktree",
+				},
+			},
+			expectedErr: "",
+		},
+		{
+			testName: "Worktree missing path",
+			repoPaths: &RepoPaths{
+				repoPath:     "/path/to/repo",
+				worktreePath: "/path/to/repo",
+			},
+			before: func(runner *oscommands.FakeCmdObjRunner, fs afero.Fs) {
+				runner.ExpectGitArgs([]string{"worktree", "list", "--porcelain"},
+					`worktree /path/to/worktree
+HEAD 775955775e79b8f5b4c4b56f82fbf657e2d5e4de
+branch refs/heads/missingbranch
+`,
+					nil)
+
+				_ = fs.MkdirAll("/path/to/repo/.git", 0o755)
+			},
+			expectedWorktrees: []*models.Worktree{
+				{
+					IsMain:        false,
+					IsCurrent:     false,
+					Path:          "/path/to/worktree",
+					IsPathMissing: true,
+					GitDir:        "",
+					Branch:        "missingbranch",
+					Name:          "worktree",
+				},
+			},
+			expectedErr: "",
+		},
+		{
+			testName: "In linked worktree",
+			repoPaths: &RepoPaths{
+				repoPath:     "/path/to/repo",
+				worktreePath: "/path/to/repo-worktree",
+			},
+			before: func(runner *oscommands.FakeCmdObjRunner, fs afero.Fs) {
+				runner.ExpectGitArgs([]string{"worktree", "list", "--porcelain"},
+					`worktree /path/to/repo
+HEAD d85cc9d281fa6ae1665c68365fc70e75e82a042d
+branch refs/heads/mybranch
+
+worktree /path/to/repo-worktree
+HEAD 775955775e79b8f5b4c4b56f82fbf657e2d5e4de
+branch refs/heads/mybranch-worktree
+`,
+					nil)
+
+				_ = fs.MkdirAll("/path/to/repo/.git", 0o755)
+				_ = fs.MkdirAll("/path/to/repo-worktree", 0o755)
+				_ = fs.MkdirAll("/path/to/repo/.git/worktrees/repo-worktree", 0o755)
+				_ = afero.WriteFile(fs, "/path/to/repo-worktree/.git", []byte("gitdir: /path/to/repo/.git/worktrees/repo-worktree"), 0o755)
+			},
+			expectedWorktrees: []*models.Worktree{
+				{
+					IsMain:        false,
+					IsCurrent:     true,
+					Path:          "/path/to/repo-worktree",
+					IsPathMissing: false,
+					GitDir:        "/path/to/repo/.git/worktrees/repo-worktree",
+					Branch:        "mybranch-worktree",
+					Name:          "repo-worktree",
+				},
+				{
+					IsMain:        true,
+					IsCurrent:     false,
+					Path:          "/path/to/repo",
+					IsPathMissing: false,
+					GitDir:        "/path/to/repo/.git",
+					Branch:        "mybranch",
+					Name:          "repo",
+				},
+			},
+			expectedErr: "",
+		},
+	}
+
+	for _, s := range scenarios {
+		s := s
+		t.Run(s.testName, func(t *testing.T) {
+			runner := oscommands.NewFakeRunner(t)
+			fs := afero.NewMemMapFs()
+			s.before(runner, fs)
+
+			loader := &WorktreeLoader{
+				GitCommon: buildGitCommon(commonDeps{runner: runner, fs: fs, repoPaths: s.repoPaths}),
+			}
+
+			worktrees, err := loader.GetWorktrees()
+			if s.expectedErr != "" {
+				assert.EqualError(t, errors.New(s.expectedErr), err.Error())
+			} else {
+				assert.NoError(t, err)
+				assert.EqualValues(t, worktrees, s.expectedWorktrees)
+			}
+		})
+	}
+}
+
 func TestGetUniqueNamesFromPaths(t *testing.T) {
 	for _, scenario := range []struct {
 		input    []string