Add test showing that a fix-it wrongly replaces parent instead of tar…

…geted child

See #15.

Tests/MacroTestingTests/FixItTests.swift

@@ -0,0 +1,92 @@
+import MacroTesting
+import SwiftDiagnostics
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxMacros
+import XCTest
+
+private enum ReplaceFirstMemberMacro: MemberMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingMembersOf declaration: some DeclGroupSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    guard
+      let nodeToReplace = declaration.memberBlock.members.first,
+      let newNode = try? MemberBlockItemSyntax(
+        decl: VariableDeclSyntax(SyntaxNodeString(stringLiteral: "\n  let oye: Oye"))
+      )
+    else { return [] }
+
+    context.diagnose(
+      Diagnostic(
+        node: node.attributeName,
+        message: SimpleDiagnosticMessage(
+          message: "First member needs to be replaced",
+          diagnosticID: MessageID(domain: "domain", id: "diagnostic2"),
+          severity: .warning
+        ),
+        fixIts: [
+          FixIt(
+            message: SimpleDiagnosticMessage(
+              message: "Replace the first member",
+              diagnosticID: MessageID(domain: "domain", id: "fixit1"),
+              severity: .error
+            ),
+            changes: [
+              .replace(oldNode: Syntax(nodeToReplace), newNode: Syntax(newNode))
+            ]
+          )
+        ]
+      )
+    )
+
+    return []
+  }
+}
+
+final class FixItTests: BaseTestCase {
+  override func invokeTest() {
+    withMacroTesting(macros: [ReplaceFirstMemberMacro.self]) {
+      super.invokeTest()
+    }
+  }
+
+  func testReplaceFirstMember_IncorrectlyReplacesParent() {
+    assertMacro {
+      """
+      @ReplaceFirstMember
+      struct FooBar {
+        let foo: Foo
+        let bar: Bar
+        let baz: Baz
+      }
+      """
+    } diagnostics: {
+      """
+      @ReplaceFirstMember
+       ┬─────────────────
+       ╰─ ⚠️ First member needs to be replaced
+          ✏️ Replace the first member
+      struct FooBar {
+        let foo: Foo
+        let bar: Bar
+        let baz: Baz
+      }
+      """
+    } fixes: {
+      """
+      @ReplaceFirstMember
+      struct FooBar {
+        let oye: Oye
+      }
+      """
+    } expansion: {
+      """
+      struct FooBar {
+        let oye: Oye
+      }
+      """
+    }
+  }
+}