test: default strategy stickiness (#4341)

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## About the changes

Unit tests for the default strategy and fallback strategy

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frontend/src/component/project/Project/ProjectSettings/ProjectDefaultStrategySettings/ProjectEnvironment/ProjectEnvironmentDefaultStrategy/EditDefaultStrategy.test.tsx

@@ -0,0 +1,55 @@
+import { screen } from '@testing-library/react';
+import { render } from 'utils/testRenderer';
+import React from 'react';
+import { useDefaultStrategy } from './EditDefaultStrategy';
+import { testServerRoute, testServerSetup } from 'utils/testServer';
+
+const server = testServerSetup();
+
+const RenderStrategy = () => {
+    const { strategy } = useDefaultStrategy('default', 'development');
+
+    return <div>{strategy?.name ?? 'no-default-strategy'}</div>;
+};
+
+const RenderFallbackStrategy = () => {
+    const { defaultStrategyFallback } = useDefaultStrategy(
+        'default',
+        'development'
+    );
+
+    return <div>{defaultStrategyFallback.parameters.stickiness}</div>;
+};
+
+test('should render default strategy from project', async () => {
+    testServerRoute(server, '/api/admin/projects/default', {
+        environments: [
+            {
+                environment: 'development',
+                defaultStrategy: { name: 'my-strategy' },
+            },
+        ],
+    });
+    render(<RenderStrategy />);
+
+    await screen.findByText('my-strategy');
+});
+
+test('should render fallback default strategy with project default stickiness', async () => {
+    testServerRoute(server, '/api/admin/projects/default', {
+        defaultStickiness: 'clientId',
+        environments: [],
+    });
+    render(<RenderFallbackStrategy />);
+
+    await screen.findByText('clientId');
+});
+
+test('should render fallback default strategy with no project default stickiness', async () => {
+    testServerRoute(server, '/api/admin/projects/default', {
+        environments: [],
+    });
+    render(<RenderFallbackStrategy />);
+
+    await screen.findByText('default');
+});

frontend/src/component/project/Project/ProjectSettings/ProjectDefaultStrategySettings/ProjectEnvironment/ProjectEnvironmentDefaultStrategy/EditDefaultStrategy.tsx

@@ -31,7 +31,7 @@ export const useDefaultStrategy = (
         constraints: [],
         parameters: {
             rollout: '100',
-            stickiness: project.defaultStickiness,
+            stickiness: project.defaultStickiness || 'default',
             groupId: '',
         },
     };