Add a check for missing test files and raise a more helpful error

.gitignore

@@ -6,5 +6,6 @@ Gopkg.toml
 
 .DS_Store
 .idea
+.vscode
 
 _artifacts

_examples/incorrect-project-structure/README.md

@@ -0,0 +1,6 @@
+This example is to help reproduce issue [#383](https://github.com/cucumber/godog/issues/383)
+
+To run the example: 
+
+    cd _examples/incorrect-project-structure
+    go run ../../cmd/godog

_examples/incorrect-project-structure/go.mod

@@ -0,0 +1,7 @@
+module incorrect-project-structure
+
+go 1.13
+
+require github.com/cucumber/godog v0.12.0
+
+replace github.com/cucumber/godog => ../../

_examples/incorrect-project-structure/main.go

@@ -0,0 +1,7 @@
+package main
+
+import "github.com/cucumber/godog"
+
+func InitializeScenario(ctx *godog.ScenarioContext) {
+
+}

internal/builder/builder.go

@@ -151,6 +151,10 @@ func Build(bin string) error {
 		break
 	}
 
+	if strings.Contains(string(testOutput), "[no test files]") {
+		return fmt.Errorf("incorrect project structure: no test files found")
+	}
+
 	// may not locate it in output
 	if workdir == testdir {
 		return fmt.Errorf("expected WORK dir path to be present in output: %s", string(testOutput))
@@ -182,6 +186,7 @@ func Build(bin string) error {
 	// we do not depend on CGO so a lot of checks are not necessary
 	linkerCfg := filepath.Join(testdir, "importcfg.link")
 	compilerCfg := linkerCfg
+
 	if vendored != nil {
 		data, err := ioutil.ReadFile(linkerCfg)
 		if err != nil {

internal/builder/builder_test.go

@@ -25,6 +25,7 @@ func Test_GodogBuild(t *testing.T) {
 	t.Run("WithinGopath", testWithinGopath)
 	t.Run("WithVendoredGodogWithoutModule", testWithVendoredGodogWithoutModule)
 	t.Run("WithVendoredGodogAndMod", testWithVendoredGodogAndMod)
+	t.Run("WithIncorrectProjectStructure", testWithIncorrectProjectStructure)
 
 	t.Run("WithModule", func(t *testing.T) {
 		t.Run("OutsideGopathAndHavingOnlyFeature", testOutsideGopathAndHavingOnlyFeature)
@@ -135,6 +136,13 @@ func main() {
 }
 `
 
+var emptyBuilderTestFile = `package godogs
+
+import "github.com/cucumber/godog"
+
+func InitializeScenario(ctx *godog.ScenarioContext) {}
+`
+
 var builderModFile = `module godogs`
 
 func buildTestPackage(dir string, files map[string]string) error {
@@ -237,6 +245,38 @@ func testWithoutTestSourceNotInGoPath(t *testing.T) {
 	builderTC.run(t)
 }
 
+func testWithIncorrectProjectStructure(t *testing.T) {
+	dir := filepath.Join(os.TempDir(), t.Name(), "godogs")
+	files := map[string]string{
+		"godogs.go": emptyBuilderTestFile,
+		"go.mod":    builderModFile,
+	}
+
+	err := buildTestPackage(dir, files)
+	defer os.RemoveAll(dir)
+	require.Nil(t, err)
+
+	prevDir, err := os.Getwd()
+	require.Nil(t, err)
+	err = os.Chdir(dir)
+	require.Nil(t, err)
+	defer os.Chdir(prevDir)
+
+	testBin, err := filepath.Abs(filepath.Join(dir, "godog.test"))
+	require.Nil(t, err)
+
+	if build.Default.GOOS == "windows" {
+		testBin += ".exe"
+	}
+
+	// call the builder - we should get an error
+	err = builder.Build(testBin)
+	// check that we even got an error at all
+	require.NotNil(t, err)
+	// now check the details of the error message
+	require.EqualError(t, err, "incorrect project structure: no test files found")
+}
+
 func testWithinGopath(t *testing.T) {
 	builderTC := builderTestCase{}