🐛 Make sure that an improperly initialised cancel store doesn't cause a panic (#657)

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### Description

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Make sure that an improperly initialised cancel store doesn't cause a
panic

### Test Coverage

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- [x]  This change is covered by existing or additional automated tests.
- [ ] Manual testing has been performed (and evidence provided) as
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documentation update).

Author: joshjennings98

changes/20250729105643.bugfix

@@ -0,0 +1 @@
+:bug: Make sure that an improperly initialised cancel store doesn't cause a panic

utils/parallelisation/cancel_functions.go

@@ -10,6 +10,9 @@ import (
 
 	"github.com/sasha-s/go-deadlock"
 	"golang.org/x/sync/errgroup"
+
+	"github.com/ARM-software/golang-utils/utils/commonerrors"
+	"github.com/ARM-software/golang-utils/utils/reflection"
 )
 
 func newFunctionStore[T any](clearOnExecution, stopOnFirstError bool, executeFunc func(context.Context, T) error) *store[T] {
@@ -45,6 +48,9 @@ func (s *store[T]) Len() int {
 func (s *store[T]) Execute(ctx context.Context) error {
 	defer s.mu.Unlock()
 	s.mu.Lock()
+	if reflection.IsEmpty(s.executeFunc) {
+		return commonerrors.New(commonerrors.ErrUndefined, "the cancel store was not initialised correctly")
+	}
 	g, gCtx := errgroup.WithContext(ctx)
 	if !s.stopOnFirstError {
 		gCtx = ctx
@@ -75,6 +81,7 @@ func (s *CancelFunctionStore) RegisterCancelFunction(cancel ...context.CancelFun
 	s.store.RegisterFunction(cancel...)
 }
 
+// Cancel will execute the cancel functions in the store. Any errors will be ignored and Execute() is recommended if you need to know if a cancellation failed
 func (s *CancelFunctionStore) Cancel() {
 	_ = s.Execute(context.Background())
 }

utils/parallelisation/cancel_functions_test.go

@@ -5,33 +5,62 @@
 package parallelisation
 
 import (
+	"context"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
+	"github.com/ARM-software/golang-utils/utils/commonerrors"
+	"github.com/ARM-software/golang-utils/utils/commonerrors/errortest"
 )
 
 // Given a CancelFunctionsStore
 // Functions can be registered
 // and all functions will be called
 func TestCancelFunctionStore(t *testing.T) {
-	// Set up some fake CancelFuncs to make sure they are called
-	called1 := false
-	called2 := false
-	cancelFunc1 := func() {
-		called1 = true
-	}
-	cancelFunc2 := func() {
-		called2 = true
-	}
+	t.Run("valid cancel store", func(t *testing.T) {
+		// Set up some fake CancelFuncs to make sure they are called
+		called1 := false
+		called2 := false
+		cancelFunc1 := func() {
+			called1 = true
+		}
+		cancelFunc2 := func() {
+			called2 = true
+		}
+
+		store := NewCancelFunctionsStore()
+
+		store.RegisterCancelFunction(cancelFunc1, cancelFunc2)
+
+		assert.Equal(t, 2, store.Len())
+
+		store.Cancel()
+
+		assert.True(t, called1)
+		assert.True(t, called2)
+	})
+
+	t.Run("incorrectly initialised cancel store", func(t *testing.T) {
+		called1 := false
+		called2 := false
+		cancelFunc1 := func() {
+			called1 = true
+		}
+		cancelFunc2 := func() {
+			called2 = true
+		}
 
-	store := NewCancelFunctionsStore()
+		store := CancelFunctionStore{}
 
-	store.RegisterCancelFunction(cancelFunc1, cancelFunc2)
+		store.RegisterCancelFunction(cancelFunc1, cancelFunc2)
 
-	assert.Equal(t, 2, store.Len())
+		assert.Equal(t, 2, store.Len())
 
-	store.Cancel()
+		err := store.Execute(context.Background())
+		errortest.AssertError(t, err, commonerrors.ErrUndefined)
 
-	assert.True(t, called1)
-	assert.True(t, called2)
+		assert.False(t, called1)
+		assert.False(t, called2)
+	})
 }