[PackageLoading] Fix linux XCTest module name

This was colliding with main package module name if there is only one
module. It got broken during the transition from `TestSuite` to `Tests`
suffix.

Author: aciidgh

Sources/PackageLoading/PackageBuilder.swift

@@ -482,10 +482,10 @@ public struct PackageBuilder {
         }
       #endif
         if !testModules.isEmpty {
-            //TODO and then we should prefix all modules with their package probably
-            //Suffix 'Tests' to test product so the module name of linux executable don't collide with
-            //main package, if present.
-            let product = Product(name: manifest.name + "Tests", type: .Test, modules: testModules)
+            // TODO and then we should prefix all modules with their package probably.
+            // Add suffix 'PackageTests' to test product so the module name of linux executable don't collide with
+            // main package, if present.
+            let product = Product(name: manifest.name + "PackageTests", type: .Test, modules: testModules)
             products.append(product)
         }
 

Tests/FunctionalTests/SwiftPMXCTestHelperTests.swift

@@ -24,7 +24,7 @@ class SwiftPMXCTestHelperTests: XCTestCase {
             // Run swift-test on package.
             XCTAssertSwiftTest(prefix)
             // Expected output dictionary.
-            let testCases = ["name": "All Tests", "tests": [["name" : "SwiftPMXCTestHelperTests.xctest",
+            let testCases = ["name": "All Tests", "tests": [["name" : "SwiftPMXCTestHelperPackageTests.xctest",
                 "tests": [
                 [
                 "name": "ObjCTests",
@@ -37,7 +37,7 @@ class SwiftPMXCTestHelperTests: XCTestCase {
               ] as Array<Dictionary<String, Any>>]] as Array<Dictionary<String, Any>>
             ] as Dictionary<String, Any> as NSDictionary
             // Run the XCTest helper tool and check result.
-            XCTAssertXCTestHelper(prefix.appending(components: ".build", "debug", "SwiftPMXCTestHelperTests.xctest"), testCases: testCases)
+            XCTAssertXCTestHelper(prefix.appending(components: ".build", "debug", "SwiftPMXCTestHelperPackageTests.xctest"), testCases: testCases)
         }
 #endif
     }

Tests/PackageLoadingTests/ConventionTests.swift

@@ -603,6 +603,62 @@ class ConventionTests: XCTestCase {
         }
     }
 
+    func testTestsProduct() throws {
+        // Make sure product name and test module name are different in single module package.
+        var fs = InMemoryFileSystem()
+        try fs.createEmptyFiles("/Sources/Foo.swift",
+                                "/Tests/FooTests/Bar.swift")
+
+        PackageBuilderTester("Foo", in: fs, products: products) { result in
+            result.checkModule("Foo") { moduleResult in
+                moduleResult.check(c99name: "Foo", type: .library, isTest: false)
+                moduleResult.checkSources(root: "/Sources", paths: "Foo.swift")
+            }
+
+            result.checkModule("FooTests") { moduleResult in
+                moduleResult.check(c99name: "FooTests", type: .library, isTest: true)
+                moduleResult.checkSources(root: "/Tests/FooTests", paths: "Bar.swift")
+            }
+
+            result.checkProduct("FooPackageTests") { productResult in
+                productResult.check(type: .Test, modules: ["FooTests"])
+            }
+        }
+
+        // Multi module tests package.
+        fs = InMemoryFileSystem()
+        try fs.createEmptyFiles("/Sources/Foo/Foo.swift",
+                                "/Sources/Bar/Bar.swift",
+                                "/Tests/FooTests/Foo.swift",
+                                "/Tests/BarTests/Bar.swift")
+
+        PackageBuilderTester("Foo", in: fs, products: products) { result in
+            result.checkModule("Foo") { moduleResult in
+                moduleResult.check(c99name: "Foo", type: .library, isTest: false)
+                moduleResult.checkSources(root: "/Sources/Foo", paths: "Foo.swift")
+            }
+
+            result.checkModule("Bar") { moduleResult in
+                moduleResult.check(c99name: "Bar", type: .library, isTest: false)
+                moduleResult.checkSources(root: "/Sources/Bar", paths: "Bar.swift")
+            }
+
+            result.checkModule("FooTests") { moduleResult in
+                moduleResult.check(c99name: "FooTests", type: .library, isTest: true)
+                moduleResult.checkSources(root: "/Tests/FooTests", paths: "Foo.swift")
+            }
+
+            result.checkModule("BarTests") { moduleResult in
+                moduleResult.check(c99name: "BarTests", type: .library, isTest: true)
+                moduleResult.checkSources(root: "/Tests/BarTests", paths: "Bar.swift")
+            }
+
+            result.checkProduct("FooPackageTests") { productResult in
+                productResult.check(type: .Test, modules: ["BarTests", "FooTests"])
+            }
+        }
+    }
+
     func testBadProducts() throws {
         var fs = InMemoryFileSystem()
         try fs.createEmptyFiles("/Foo.swift")
@@ -789,6 +845,7 @@ class ConventionTests: XCTestCase {
         ("testManifestTargetDeclErrors", testManifestTargetDeclErrors),
         ("testProducts", testProducts),
         ("testBadProducts", testBadProducts),
+        ("testTestsProduct", testTestsProduct),
     ]
 }