Use a file replacement visitor to test mutation

Author: danielctull

Package.swift

@@ -59,6 +59,7 @@ let package = Package(
         "PackageKit",
         "SyntaxMutation",
         .product(name: "SwiftSyntax", package: "swift-syntax"),
+        .product(name: "SwiftSyntaxBuilder", package: "swift-syntax"),
       ],
     ),
 

Tests/SyntaxMutationTests/SyntaxMutationTests.swift

@@ -1,112 +1,40 @@
 import CoreMutation
 @testable import PackageKit
 import SwiftSyntax
+import SwiftSyntaxBuilder
 import SyntaxMutation
 import Testing
 
 @Suite("SwiftSyntax Mutation")
 struct SyntaxMutationTests {
 
-  @Test("empty")
-  func empty() {
-    let file = Source.File(name: "name", path: "path", code: "")
-    let mutants = Mutation.reverseString.mutants(for: file)
-    #expect(mutants.isEmpty)
-  }
-
   @Test("single")
   func single() throws {
 
-    let file = Source.File(name: "name", path: "path", code: """
-      func foo() {
-        print("hello!")
-      }
-      """)
+    final class Visitor: MutationVisitor {
 
-    let mutants = Mutation.reverseString.mutants(for: file)
-
-    try #require(mutants.count == 1)
-    #expect(mutants[0].original == file.code)
-    #expect(mutants[0].mutation == "Reverse String")
-    #expect(mutants[0].location.name == file.name)
-    #expect(mutants[0].location.path == file.path)
-    #expect(mutants[0].location.start == Source.Position(line: 2, column: 10, offset: 22))
-    #expect(mutants[0].location.end == Source.Position(line: 2, column: 16, offset: 28))
-    #expect(mutants[0].replacement == """
-      func foo() {
-        print("!olleh")
+      override func visit(_ node: CodeBlockItemListSyntax) -> SyntaxVisitorContinueKind {
+        record(before: node, after: ExprSyntax("""
+          let name = "Daniel"
+          """))
+        return super.visit(node)
       }
-      """)
-  }
-
-  @Test("multiple")
-  func multiple() throws {
+    }
 
-    let file = Source.File(name: "name", path: "path", code: """
-      func foo() {
-        print("hello!")
-      }
-      
-      var bar: String { "baz" }
-      """)
+    let mutation = Mutation(name: "Replace File", visitor: Visitor.self)
+    let file = Source.File(name: "name", path: "path", code: "")
 
-    let mutants = Mutation.reverseString.mutants(for: file)
+    let mutants = mutation.mutants(for: file)
 
-    try #require(mutants.count == 2)
+    try #require(mutants.count == 1)
     #expect(mutants[0].original == file.code)
-    #expect(mutants[0].mutation == "Reverse String")
+    #expect(mutants[0].mutation == mutation.name)
     #expect(mutants[0].location.name == file.name)
     #expect(mutants[0].location.path == file.path)
-    #expect(mutants[0].location.start == Source.Position(line: 2, column: 10, offset: 22))
-    #expect(mutants[0].location.end == Source.Position(line: 2, column: 16, offset: 28))
+    #expect(mutants[0].location.start == Source.Position(line: 1, column: 1, offset: 0))
+    #expect(mutants[0].location.end == Source.Position(line: 1, column: 1, offset: 0))
     #expect(mutants[0].replacement == """
-      func foo() {
-        print("!olleh")
-      }
-      
-      var bar: String { "baz" }
-      """)
-
-    #expect(mutants[1].original == file.code)
-    #expect(mutants[1].mutation == "Reverse String")
-    #expect(mutants[1].location.name == file.name)
-    #expect(mutants[1].location.path == file.path)
-    #expect(mutants[1].location.start == Source.Position(line: 5, column: 20, offset: 53))
-    #expect(mutants[1].location.end == Source.Position(line: 5, column: 23, offset: 56))
-    #expect(mutants[1].replacement == """
-      func foo() {
-        print("hello!")
-      }
-      
-      var bar: String { "zab" }
+      let name = "Daniel"
       """)
   }
 }
-
-extension Mutation {
-
-  fileprivate static let reverseString = Mutation(
-    name: "Reverse String",
-    visitor: ReverseString.self,
-  )
-}
-
-final private class ReverseString: MutationVisitor {
-
-  override func visit(_ node: StringLiteralExprSyntax) -> SyntaxVisitorContinueKind {
-
-    for segment in node.segments {
-      switch segment {
-      case .expressionSegment:
-        continue
-
-      case .stringSegment(let before):
-        let new = String(before.content.text.reversed())
-        let after = StringSegmentSyntax(content: .stringSegment(new))
-        record(before: before, after: after)
-      }
-    }
-
-    return super.visit(node)
-  }
-}