Add test for checking out a file from a commit

This works, we just didn't have a test for it.

pkg/integration/tests/commit/checkout_file_from_commit.go

@@ -0,0 +1,55 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CheckoutFileFromCommit = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Checkout a file from a commit",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file.txt", "one\n")
+		shell.Commit("one")
+		shell.CreateFileAndAdd("file.txt", "two\n")
+		shell.Commit("two")
+		shell.CreateFileAndAdd("file.txt", "three\n")
+		shell.Commit("three")
+		shell.CreateFileAndAdd("file.txt", "four\n")
+		shell.Commit("four")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("four").IsSelected(),
+				Contains("three"),
+				Contains("two"),
+				Contains("one"),
+			).
+			NavigateToLine(Contains("three")).
+			Tap(func() {
+				t.Views().Main().ContainsLines(
+					Contains("-two"),
+					Contains("+three"),
+				)
+			}).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Equals("M file.txt"),
+			).
+			Press(keys.CommitFiles.CheckoutCommitFile)
+
+		t.Views().Files().
+			Lines(
+				Equals("M  file.txt"),
+			)
+
+		t.FileSystem().FileContent("file.txt", Equals("three\n"))
+	},
+})

pkg/integration/tests/test_list.go

@@ -89,6 +89,7 @@ var tests = []*components.IntegrationTest{
 	commit.AmendWhenThereAreConflictsAndContinue,
 	commit.AutoWrapMessage,
 	commit.Checkout,
+	commit.CheckoutFileFromCommit,
 	commit.Commit,
 	commit.CommitMultiline,
 	commit.CommitSkipHooks,