Fix panic on nil AS/ASR marhsal + add test

pkg/kubecost/allocation.go

@@ -1889,6 +1889,9 @@ func (as *AllocationSet) Map() map[string]*Allocation {
 
 // MarshalJSON JSON-encodes the AllocationSet
 func (as *AllocationSet) MarshalJSON() ([]byte, error) {
+	if as == nil {
+		return json.Marshal(map[string]*Allocation{})
+	}
 	as.RLock()
 	defer as.RUnlock()
 	return json.Marshal(as.allocations)
@@ -2224,6 +2227,10 @@ func (asr *AllocationSetRange) Length() int {
 
 // MarshalJSON JSON-encodes the range
 func (asr *AllocationSetRange) MarshalJSON() ([]byte, error) {
+	if asr == nil {
+		return json.Marshal([]*AllocationSet{})
+	}
+
 	asr.RLock()
 	defer asr.RUnlock()
 	return json.Marshal(asr.allocations)

pkg/kubecost/allocation_test.go

@@ -2368,8 +2368,60 @@ func TestAllocationSetRange_InsertRange(t *testing.T) {
 // TODO niko/etl
 // func TestAllocationSetRange_Length(t *testing.T) {}
 
-// TODO niko/etl
-// func TestAllocationSetRange_MarshalJSON(t *testing.T) {}
+func TestAllocationSetRange_MarshalJSON(t *testing.T) {
+
+	tests := []struct {
+		name     string
+		arg      *AllocationSetRange
+		expected *AllocationSetRange
+	}{
+		{
+			name: "Nil ASR",
+			arg:  nil,
+		},
+		{
+			name: "Nil AS in ASR",
+			arg:  NewAllocationSetRange(nil),
+		},
+		{
+			name: "Normal ASR",
+			arg: &AllocationSetRange{
+				allocations: []*AllocationSet{
+					{
+						allocations: map[string]*Allocation{
+							"a": {
+								Start: time.Now().UTC().Truncate(day),
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+
+		bytes, err := json.Marshal(test.arg)
+		if err != nil {
+			t.Fatalf("ASR Marshal: test %s, unexpected error: %s", test.name, err)
+		}
+
+		var testASR []*AllocationSet
+		marshaled := &testASR
+
+		err = json.Unmarshal(bytes, marshaled)
+
+		if err != nil {
+			t.Fatalf("ASR Unmarshal: test %s: unexpected error: %s", test.name, err)
+		}
+
+		if test.arg.Length() != len(testASR) {
+			t.Fatalf("ASR Unmarshal: test %s: length mutated in encoding: expected %d but got %d", test.name, test.arg.Length(), len(testASR))
+		}
+
+		// Allocations don't unmarshal back from json
+	}
+}
 
 // TODO niko/etl
 // func TestAllocationSetRange_Slice(t *testing.T) {}