Drop mutants that contain no source changes

Author: danielctull

Sources/CoreMutation/Mutation.swift

@@ -33,6 +33,7 @@ extension Mutation {
           replacement: $0.mutate()
         )
       }
+      .drop { $0.replacement == file.code }
       .uniqued(on: \.replacement)
 
     return Array(mutants)

Tests/CoreMutationTests/MutationTests.swift

@@ -16,8 +16,8 @@ struct MutationTests {
       #expect(mutants.isEmpty)
     }
 
-    @Test("no change")
-    func noChange() throws {
+    @Test("change")
+    func change() throws {
 
       let mutation = Mutation(name: "test") { file in
         [Mutation.Change(start: .start, end: .end) { "replacement" }]
@@ -34,6 +34,18 @@ struct MutationTests {
       #expect(mutants[0].original == "original")
       #expect(mutants[0].replacement == "replacement")
     }
+
+    @Test("no changes")
+    func noChanges() throws {
+
+      let mutation = Mutation(name: "test") { file in
+        [Mutation.Change(start: .start, end: .end) { file.code }]
+      }
+
+      let file = Source.File(name: "name", path: "path", code: "original")
+      let mutants = mutation.mutants(for: file)
+      #expect(mutants.isEmpty)
+    }
   }
 
   @Suite("Name")

Tests/SyntaxMutationTests/SyntaxMutationTests.swift

@@ -70,4 +70,24 @@ struct SyntaxMutationTests {
       let name = "Daniel"
       """)
   }
+
+  @Test("non changes are not counted")
+  func nonChanges() {
+
+    final class Visitor: MutationVisitor {
+
+      override func visit(_ node: CodeBlockItemListSyntax) -> SyntaxVisitorContinueKind {
+        record(before: node, after: node)
+        return super.visit(node)
+      }
+    }
+
+    let mutation = Mutation(name: "Replace File", visitor: Visitor.self)
+    let file = Source.File(name: "name", path: "path", code: """
+      let name = "Daniel"
+      """)
+
+    let mutants = mutation.mutants(for: file)
+    #expect(mutants.isEmpty)
+  }
 }