Add new final_test_case rule (#5396)

.swiftlint.yml

@@ -21,6 +21,7 @@ disabled_rules:
   - explicit_top_level_acl
   - explicit_type_interface
   - file_types_order
+  - final_test_case
   - force_unwrapping
   - function_default_parameter_at_end
   - implicit_return

CHANGELOG.md

@@ -31,6 +31,9 @@
 * Print invalid keys when configuration parsing fails.  
   [SimplyDanny](https://github.com/SimplyDanny)
   [#5347](https://github.com/realm/SwiftLint/pull/5347)
+
+* Add new `final_test_case` rule that triggers on non-final test classes.  
+  [SimplyDanny](https://github.com/SimplyDanny)
 
 * Allow to configure more operators in `identifier_name` rule. The new option
   is named `additional_operators`. Use it to add more operators to the list

Source/SwiftLintBuiltInRules/Models/BuiltInRules.swift

@@ -71,6 +71,7 @@ public let builtInRules: [any Rule.Type] = [
     FileNameNoSpaceRule.self,
     FileNameRule.self,
     FileTypesOrderRule.self,
+    FinalTestCaseRule.self,
     FirstWhereRule.self,
     FlatMapOverMapReduceRule.self,
     ForWhereRule.self,

Source/SwiftLintBuiltInRules/Rules/Performance/FinalTestCaseRule.swift

@@ -0,0 +1,87 @@
+import SwiftLintCore
+import SwiftSyntax
+
+@SwiftSyntaxRule
+struct FinalTestCaseRule: SwiftSyntaxCorrectableRule, OptInRule {
+    var configuration = FinalTestCaseConfiguration()
+
+    static var description = RuleDescription(
+        identifier: "final_test_case",
+        name: "Final Test Case",
+        description: "Test cases should be final",
+        kind: .performance,
+        nonTriggeringExamples: [
+            Example("final class Test: XCTestCase {}"),
+            Example("open class Test: XCTestCase {}"),
+            Example("public final class Test: QuickSpec {}"),
+            Example("class Test: MyTestCase {}"),
+            Example("struct Test: MyTestCase {}", configuration: ["test_parent_classes": "MyTestCase"])
+        ],
+        triggeringExamples: [
+            Example("class ↓Test: XCTestCase {}"),
+            Example("public class ↓Test: QuickSpec {}"),
+            Example("class ↓Test: MyTestCase {}", configuration: ["test_parent_classes": "MyTestCase"])
+        ],
+        corrections: [
+            Example("class ↓Test: XCTestCase {}"):
+                Example("final class Test: XCTestCase {}"),
+            Example("internal class ↓Test: XCTestCase {}"):
+                Example("internal final class Test: XCTestCase {}")
+        ]
+    )
+
+    func makeRewriter(file: SwiftLintFile) -> (some ViolationsSyntaxRewriter)? {
+       Rewriter(
+           configuration: configuration,
+           locationConverter: file.locationConverter,
+           disabledRegions: disabledRegions(file: file)
+       )
+   }
+}
+
+private extension FinalTestCaseRule {
+    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
+        override func visitPost(_ node: ClassDeclSyntax) {
+            if node.isNonFinalTestClass(parentClasses: configuration.testParentClasses) {
+                violations.append(node.name.positionAfterSkippingLeadingTrivia)
+            }
+        }
+    }
+
+    final class Rewriter: ViolationsSyntaxRewriter {
+        private let configuration: FinalTestCaseConfiguration
+
+        init(configuration: FinalTestCaseConfiguration,
+             locationConverter: SourceLocationConverter,
+             disabledRegions: [SourceRange]) {
+            self.configuration = configuration
+            super.init(locationConverter: locationConverter, disabledRegions: disabledRegions)
+        }
+
+        override func visit(_ node: ClassDeclSyntax) -> DeclSyntax {
+            var newNode = node
+            if node.isNonFinalTestClass(parentClasses: configuration.testParentClasses) {
+                correctionPositions.append(node.name.positionAfterSkippingLeadingTrivia)
+                let finalModifier = DeclModifierSyntax(name: .keyword(.final))
+                newNode =
+                    if node.modifiers.isEmpty {
+                        node
+                            .with(\.modifiers, [finalModifier.with(\.leadingTrivia, node.classKeyword.leadingTrivia)])
+                            .with(\.classKeyword.leadingTrivia, .space)
+                    } else {
+                        node
+                            .with(\.modifiers, node.modifiers + [finalModifier.with(\.trailingTrivia, .space)])
+                    }
+            }
+            return super.visit(newNode)
+        }
+    }
+}
+
+private extension ClassDeclSyntax {
+    func isNonFinalTestClass(parentClasses: Set<String>) -> Bool {
+           inheritanceClause.containsInheritedType(inheritedTypes: parentClasses)
+        && !modifiers.contains(keyword: .open)
+        && !modifiers.contains(keyword: .final)
+    }
+}

Source/SwiftLintBuiltInRules/Rules/RuleConfigurations/UnitTestConfiguration.swift

@@ -2,8 +2,9 @@ import SwiftLintCore
 
 typealias BalancedXCTestLifecycleConfiguration = UnitTestConfiguration<BalancedXCTestLifecycleRule>
 typealias EmptyXCTestMethodConfiguration = UnitTestConfiguration<EmptyXCTestMethodRule>
-typealias SingleTestClassConfiguration = UnitTestConfiguration<SingleTestClassRule>
+typealias FinalTestCaseConfiguration = UnitTestConfiguration<FinalTestCaseRule>
 typealias NoMagicNumbersConfiguration = UnitTestConfiguration<NoMagicNumbersRule>
+typealias SingleTestClassConfiguration = UnitTestConfiguration<SingleTestClassRule>
 
 @AutoApply
 struct UnitTestConfiguration<Parent: Rule>: SeverityBasedRuleConfiguration {

Tests/GeneratedTests/GeneratedTests.swift

@@ -416,6 +416,12 @@ class FileTypesOrderRuleGeneratedTests: SwiftLintTestCase {
     }
 }
 
+class FinalTestCaseRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(FinalTestCaseRule.description)
+    }
+}
+
 class FirstWhereRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(FirstWhereRule.description)