libcontainer/intelrdt: fix unit tests

Signed-off-by: Markus Lehtonen <[email protected]>

Author: marquiz

libcontainer/intelrdt/intelrdt.go

@@ -326,14 +326,19 @@ func getIntelRdtParamString(path, file string) (string, error) {
 	return string(bytes.TrimSpace(contents)), nil
 }
 
-func writeFile(dir, file, data string) error {
-	if dir == "" {
-		return fmt.Errorf("no such directory for %s", file)
-	}
-	if err := os.WriteFile(filepath.Join(dir, file), []byte(data+"\n"), 0o600); err != nil {
-		return newLastCmdError(fmt.Errorf("intelrdt: unable to write %v: %w", data, err))
+var writeFile = writeFileFunc(os.WriteFile)
+
+// writeFileFunc is a helper to allow mocking os.WriteFile in tests.
+func writeFileFunc(f func(string, []byte, os.FileMode) error) func(string, string, string) error {
+	return func(dir, file, data string) error {
+		if dir == "" {
+			return fmt.Errorf("no such directory for %s", file)
+		}
+		if err := f(filepath.Join(dir, file), []byte(data+"\n"), 0o600); err != nil {
+			return newLastCmdError(fmt.Errorf("intelrdt: unable to write %v: %w", data, err))
+		}
+		return nil
 	}
-	return nil
 }
 
 // Get the read-only L3 cache information

libcontainer/intelrdt/intelrdt_test.go

@@ -102,16 +102,24 @@ func TestIntelRdtSet(t *testing.T) {
 		},
 	}
 
+	// override writeFile to validate all writes
+	writeFile = writeFileFunc(func(name string, data []byte, perm os.FileMode) error {
+		f, err := os.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_APPEND, perm)
+		if err != nil {
+			return err
+		}
+		_, err = f.Write(data)
+		if errc := f.Close(); errc != nil && err == nil {
+			err = errc
+		}
+		return err
+	})
+
 	for _, tc := range tcs {
 		t.Run(tc.name, func(t *testing.T) {
 			helper := NewIntelRdtTestUtil(t)
 			helper.config.IntelRdt = tc.config
 
-			helper.writeFileContents(map[string]string{
-				/* Common initial value for all test cases */
-				"schemata": "MB:0=100\nL3:0=ffff\nL2:0=ffffffff\n",
-			})
-
 			intelrdt := newManager(helper.config, "", helper.IntelRdtPath)
 			if err := intelrdt.Set(helper.config); err != nil {
 				t.Fatal(err)