test: add test case for SystemJS default import fix

- Add comprehensive test case for system-default-import-fix
- Test both scenarios: modules with and without default property
- Verify default imports work correctly for SystemJS externals
- Ensure backward compatibility with existing functionality

test/configCases/target/system-default-import-fix/index.js

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+import React, { useEffect } from "react";
+
+/* This test verifies that default imports work correctly with SystemJS externals
+ * when the external module doesn't have a default property (e.g., React)
+ */
+
+it("should correctly handle default import from SystemJS external", function() {
+	// React should be the entire module object, not undefined
+	expect(React).toBeDefined();
+	expect(typeof React).toBe("object");
+	expect(React.Component).toBeDefined();
+	expect(React.Fragment).toBeDefined();
+	
+	// Named imports should still work
+	expect(typeof useEffect).toBe("function");
+	
+	// The default import should not be undefined
+	expect(React).not.toBeUndefined();
+});

test/configCases/target/system-default-import-fix/react-with-default.js

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+// Mock React module that HAS a default property
+// This simulates ES6 modules with default exports
+const React = {
+	Component: function Component() {},
+	Fragment: Symbol("react.fragment"),
+	Profiler: Symbol("react.profiler"),
+	useEffect: function useEffect(callback, deps) {
+		return callback();
+	},
+	useState: function useState(initial) {
+		return [initial, function() {}];
+	},
+	createElement: function createElement(type, props, ...children) {
+		return { type, props, children };
+	}
+};
+
+// Export with default property (ES6 module format)
+module.exports = React;
+module.exports.default = React;
+module.exports.useEffect = React.useEffect;
+module.exports.Component = React.Component;
+module.exports.Fragment = React.Fragment;
+module.exports.Profiler = React.Profiler;
+module.exports.useState = React.useState;
+module.exports.createElement = React.createElement;

test/configCases/target/system-default-import-fix/react.js

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+// Mock React module that doesn't have a default property
+// This simulates how React is typically exported in SystemJS environments
+const React = {
+	Component: function Component() {},
+	Fragment: Symbol("react.fragment"),
+	Profiler: Symbol("react.profiler"),
+	useEffect: function useEffect(callback, deps) {
+		return callback();
+	},
+	useState: function useState(initial) {
+		return [initial, function() {}];
+	},
+	createElement: function createElement(type, props, ...children) {
+		return { type, props, children };
+	}
+};
+
+// Export named exports (SystemJS style - no default property)
+module.exports = React;
+module.exports.useEffect = React.useEffect;
+module.exports.Component = React.Component;
+module.exports.Fragment = React.Fragment;
+module.exports.Profiler = React.Profiler;
+module.exports.useState = React.useState;
+module.exports.createElement = React.createElement;

test/configCases/target/system-default-import-fix/test.config.js

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+"use strict";
+
+const path = require("path");
+
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	entry: "./test.js",
+	output: {
+		path: path.resolve(__dirname, "dist"),
+		filename: "bundle.js",
+		libraryTarget: "system"
+	},
+	externals: {
+		react: "react",
+		"react-with-default": "react-with-default"
+	},
+	resolve: {
+		alias: {
+			react: path.resolve(__dirname, "react.js"),
+			"react-with-default": path.resolve(__dirname, "react-with-default.js")
+		}
+	},
+	node: {
+		__dirname: false,
+		__filename: false
+	}
+};

test/configCases/target/system-default-import-fix/test.js

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+import React, { useEffect } from "react";
+import ReactWithDefault, { useEffect as useEffectWithDefault } from "react-with-default";
+
+/* This test verifies that default imports work correctly with SystemJS externals
+ * in both scenarios:
+ * 1. External module without default property (traditional SystemJS)
+ * 2. External module with default property (ES6 module format)
+ */
+
+it("should correctly handle default import from SystemJS external without default property", function() {
+	// React should be the entire module object, not undefined
+	expect(React).toBeDefined();
+	expect(typeof React).toBe("object");
+	expect(React.Component).toBeDefined();
+	expect(React.Fragment).toBeDefined();
+	
+	// Named imports should still work
+	expect(typeof useEffect).toBe("function");
+	
+	// The default import should not be undefined
+	expect(React).not.toBeUndefined();
+});
+
+it("should correctly handle default import from SystemJS external with default property", function() {
+	// ReactWithDefault should be the default property value
+	expect(ReactWithDefault).toBeDefined();
+	expect(typeof ReactWithDefault).toBe("object");
+	expect(ReactWithDefault.Component).toBeDefined();
+	expect(ReactWithDefault.Fragment).toBeDefined();
+	
+	// Named imports should still work
+	expect(typeof useEffectWithDefault).toBe("function");
+	
+	// The default import should not be undefined
+	expect(ReactWithDefault).not.toBeUndefined();
+});

test/configCases/target/system-default-import-fix/webpack.config.js

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+"use strict";
+
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	output: {
+		libraryTarget: "system"
+	},
+	externals: {
+		react: "react"
+	},
+	node: {
+		__dirname: false,
+		__filename: false
+	}
+};