pkg/atomicwriter: refactor tests

- rename tests to match the function tested
- remove init func in favor or a test-helper
- rename some vars to prevent shadowing
- update example values to be more descriptive
- add a utility for asserting file content and mode

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/atomicwriter/atomicwriter_test.go

@@ -2,48 +2,57 @@ package atomicwriter
 
 import (
 	"bytes"
+	"errors"
 	"os"
 	"path/filepath"
 	"runtime"
 	"testing"
 )
 
-var testMode os.FileMode = 0o640
-
-func init() {
-	// Windows does not support full Linux file mode
+// testMode returns the file-mode to use in tests, accounting for Windows
+// not supporting full Linux file mode.
+func testMode() os.FileMode {
 	if runtime.GOOS == "windows" {
-		testMode = 0o666
+		return 0o666
 	}
+	return 0o640
 }
 
-func TestAtomicWriteToFile(t *testing.T) {
-	tmpDir := t.TempDir()
-
-	expected := []byte("barbaz")
-	if err := WriteFile(filepath.Join(tmpDir, "foo"), expected, testMode); err != nil {
-		t.Fatalf("Error writing to file: %v", err)
-	}
-
-	actual, err := os.ReadFile(filepath.Join(tmpDir, "foo"))
+// assertFile asserts the given fileName to exist, and to have the expected
+// content and mode.
+func assertFile(t *testing.T, fileName string, fileContent []byte, expectedMode os.FileMode) {
+	t.Helper()
+	actual, err := os.ReadFile(fileName)
 	if err != nil {
 		t.Fatalf("Error reading from file: %v", err)
 	}
 
-	if !bytes.Equal(actual, expected) {
-		t.Fatalf("Data mismatch, expected %q, got %q", expected, actual)
+	if !bytes.Equal(actual, fileContent) {
+		t.Errorf("Data mismatch, expected %q, got %q", fileContent, actual)
 	}
 
-	st, err := os.Stat(filepath.Join(tmpDir, "foo"))
+	st, err := os.Stat(fileName)
 	if err != nil {
 		t.Fatalf("Error statting file: %v", err)
 	}
-	if expected := testMode; st.Mode() != expected {
-		t.Fatalf("Mode mismatched, expected %o, got %o", expected, st.Mode())
+	if st.Mode() != expectedMode {
+		t.Errorf("Mode mismatched, expected %o, got %o", expectedMode, st.Mode())
 	}
 }
 
-func TestAtomicWriteSetCommit(t *testing.T) {
+func TestWriteFile(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	fileName := filepath.Join(tmpDir, "test.txt")
+	fileContent := []byte("file content")
+	fileMode := testMode()
+	if err := WriteFile(fileName, fileContent, fileMode); err != nil {
+		t.Fatalf("Error writing to file: %v", err)
+	}
+	assertFile(t, fileName, fileContent, fileMode)
+}
+
+func TestWriteSetCommit(t *testing.T) {
 	tmpDir := t.TempDir()
 
 	if err := os.Mkdir(filepath.Join(tmpDir, "tmp"), 0o700); err != nil {
@@ -56,8 +65,10 @@ func TestAtomicWriteSetCommit(t *testing.T) {
 		t.Fatalf("Error creating atomic write set: %s", err)
 	}
 
-	expected := []byte("barbaz")
-	if err := ws.WriteFile("foo", expected, testMode); err != nil {
+	fileContent := []byte("file content")
+	fileMode := testMode()
+
+	if err := ws.WriteFile("foo", fileContent, fileMode); err != nil {
 		t.Fatalf("Error writing to file: %v", err)
 	}
 
@@ -69,25 +80,10 @@ func TestAtomicWriteSetCommit(t *testing.T) {
 		t.Fatalf("Error committing file: %s", err)
 	}
 
-	actual, err := os.ReadFile(filepath.Join(targetDir, "foo"))
-	if err != nil {
-		t.Fatalf("Error reading from file: %v", err)
-	}
-
-	if !bytes.Equal(actual, expected) {
-		t.Fatalf("Data mismatch, expected %q, got %q", expected, actual)
-	}
-
-	st, err := os.Stat(filepath.Join(targetDir, "foo"))
-	if err != nil {
-		t.Fatalf("Error statting file: %v", err)
-	}
-	if expected := testMode; st.Mode() != expected {
-		t.Fatalf("Mode mismatched, expected %o, got %o", expected, st.Mode())
-	}
+	assertFile(t, filepath.Join(targetDir, "foo"), fileContent, fileMode)
 }
 
-func TestAtomicWriteSetCancel(t *testing.T) {
+func TestWriteSetCancel(t *testing.T) {
 	tmpDir := t.TempDir()
 
 	if err := os.Mkdir(filepath.Join(tmpDir, "tmp"), 0o700); err != nil {
@@ -99,8 +95,9 @@ func TestAtomicWriteSetCancel(t *testing.T) {
 		t.Fatalf("Error creating atomic write set: %s", err)
 	}
 
-	expected := []byte("barbaz")
-	if err := ws.WriteFile("foo", expected, testMode); err != nil {
+	fileContent := []byte("file content")
+	fileMode := testMode()
+	if err := ws.WriteFile("foo", fileContent, fileMode); err != nil {
 		t.Fatalf("Error writing to file: %v", err)
 	}
 
@@ -110,7 +107,7 @@ func TestAtomicWriteSetCancel(t *testing.T) {
 
 	if _, err := os.ReadFile(filepath.Join(tmpDir, "target", "foo")); err == nil {
 		t.Fatalf("Expected error reading file where should not exist")
-	} else if !os.IsNotExist(err) {
+	} else if !errors.Is(err, os.ErrNotExist) {
 		t.Fatalf("Unexpected error reading file: %s", err)
 	}
 }