Add tests for product with missing modules

Author: aciidgh

Fixtures/Miscellaneous/ProductWithMissingModules/Foo.swift

@@ -0,0 +1,3 @@
+public class Foo {
+    var bar: Int = 0
+}

Fixtures/Miscellaneous/ProductWithMissingModules/Package.swift

@@ -0,0 +1,7 @@
+import PackageDescription
+
+let package = Package(name: "Foo")
+
+let archive = Product(name: "Bar", type: .Library(.Static), modules: "Foo", "Baz")
+
+products.append(archive)

Fixtures/Miscellaneous/ProductWithNoModules/Foo.swift

@@ -0,0 +1,3 @@
+public class Foo {
+    var bar: Int = 0
+}

Fixtures/Miscellaneous/ProductWithNoModules/Package.swift

@@ -0,0 +1,7 @@
+import PackageDescription
+
+let package = Package(name: "Foo")
+
+let archive = Product(name: "Bar", type: .Library(.Dynamic), modules: "")
+
+products.append(archive)

Tests/Functional/TestMiscellaneous.swift

@@ -349,4 +349,17 @@ class MiscellaneousTestCase: XCTestCase {
             XCTAssertFileExists(prefix, ".build/debug/libBar.a")
         }
     }
+    
+    func testProductWithNoModules() {
+        fixture(name: "Miscellaneous/ProductWithNoModules") { prefix in
+            XCTAssertBuildFails(prefix)
+        }
+    }
+    
+    func testProductWithMissingModules() {
+        fixture(name: "Miscellaneous/ProductWithMissingModules") { prefix in
+            XCTAssertBuilds(prefix)
+            XCTAssertFileExists(prefix, ".build/debug/libBar.a")
+        }
+    }
 }