Refactor database layer: convert to DatabaseProvider class with initialization

test/server_test.dart

@@ -0,0 +1,39 @@
+import 'dart:io';
+
+import 'package:http/http.dart';
+import 'package:test/test.dart';
+
+void main() {
+  final port = '8080';
+  final host = 'http://0.0.0.0:$port';
+  late Process p;
+
+  setUp(() async {
+    p = await Process.start(
+      'dart',
+      ['run', 'bin/server.dart'],
+      environment: {'PORT': port},
+    );
+    // Wait for server to start and print to stdout.
+    await p.stdout.first;
+  });
+
+  tearDown(() => p.kill());
+
+  test('Root', () async {
+    final response = await get(Uri.parse('$host/'));
+    expect(response.statusCode, 200);
+    expect(response.body, 'Hello, World!\n');
+  });
+
+  test('Echo', () async {
+    final response = await get(Uri.parse('$host/echo/hello'));
+    expect(response.statusCode, 200);
+    expect(response.body, 'hello\n');
+  });
+
+  test('404', () async {
+    final response = await get(Uri.parse('$host/foobar'));
+    expect(response.statusCode, 404);
+  });
+}