feat: Working on node builder

Tests/CliDocTests/CliDocTests.swift

@@ -0,0 +1,70 @@
+@_spi(Internal) import CliDoc
+import Testing
+
+@Test
+func testNodeBuilder() {
+  let node = AnyNode {
+    Text("foo").color(.green).style(.bold)
+    NewLine()
+    Text("bar").repeating(2)
+  }
+  let expected = """
+  \("foo".green.bold)
+  barbar
+  """
+  #expect(node.render() == expected)
+}
+
+@Test(
+  arguments: [
+    (true, "foo bar"),
+    (false, """
+    foo
+    bar
+    """)
+  ]
+)
+func testSection(
+  inline: Bool,
+  expected: String
+) {
+  let node = AnyNode {
+    Section(
+      header: "foo",
+      separator: inline ? Space().eraseToAnyNode() : NewLine().eraseToAnyNode()
+    ) {
+      Text("bar")
+    }
+  }
+
+  print(node.render())
+  #expect(node.render() == expected)
+}
+
+@Test
+func testHeader() {
+  let header = Header("Foo")
+  let expected = "\("Foo".yellow.bold)"
+  #expect(header.render() == expected)
+}
+
+@Test
+func testGroup() {
+  let group = Group {
+    Text("foo")
+    Text("bar")
+  }
+
+  print(group.render())
+  #expect(group.render() == "foo bar")
+
+  let group2 = Group(separator: .newLine()) {
+    Text("foo")
+    Text("bar")
+  }
+  let expected = """
+  foo
+  bar
+  """
+  #expect(group2.render() == expected)
+}