adding test cases for the new func

Author: komer3

cloud/nodeipam/ipam/cloud_allocator_test.go

@@ -50,6 +50,54 @@ type testCase struct {
 	instance       *linodego.Instance
 }
 
+func TestComputeStableIPv6PodCIDR(t *testing.T) {
+	for _, tc := range []struct {
+		name        string
+		baseCIDR    string
+		desiredMask int
+		wantCIDR    string
+		wantOK      bool
+	}{
+		{name: "nil base", baseCIDR: "", desiredMask: 112, wantOK: false},
+		{name: "non-/112 desired", baseCIDR: "2300:5800:2:1::/64", desiredMask: 120, wantOK: false},
+		{name: "ipv4 base", baseCIDR: "10.0.0.0/24", desiredMask: 112, wantOK: false},
+		{name: "non-/64 ipv6 base (/56)", baseCIDR: "2300:5800:2::/56", desiredMask: 112, wantOK: false},
+		{name: "success /64 -> mnemonic /112", baseCIDR: "2300:5800:2:1::/64", desiredMask: 112, wantCIDR: "2300:5800:2:1:0:c::/112", wantOK: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var baseNet *net.IPNet
+			if tc.baseCIDR != "" {
+				_, parsed, err := net.ParseCIDR(tc.baseCIDR)
+				if err != nil {
+					t.Fatalf("parse base cidr: %v", err)
+				}
+				baseNet = parsed
+			}
+			got, ok := getIPv6PodCIDR(baseNet, tc.desiredMask)
+			if ok != tc.wantOK {
+				t.Fatalf("ok mismatch: got %v want %v (gotCIDR=%v)", ok, tc.wantOK, func() string {
+					if got != nil {
+						return got.String()
+					}
+					return ""
+				}())
+			}
+			if !tc.wantOK {
+				if got != nil {
+					t.Fatalf("expected nil cidr on failure, got %v", got.String())
+				}
+				return
+			}
+			if got == nil {
+				t.Fatalf("expected non-nil cidr")
+			}
+			if got.String() != tc.wantCIDR {
+				t.Fatalf("cidr mismatch: got %s want %s", got.String(), tc.wantCIDR)
+			}
+		})
+	}
+}
+
 func TestGetIPv6RangeFromLinodeInterface(t *testing.T) {
 	for _, tc := range []struct {
 		iface         linodego.LinodeInterface