Reproduce build failure for TestMain in black box test

#32

main_test.go

@@ -466,6 +466,16 @@ func Test_gobcoMain__TestMain(t *testing.T) {
 	_ = stderr
 }
 
+func Test_gobcoMain__TestMainTest(t *testing.T) {
+	s := NewSuite(t)
+	defer s.TearDownTest()
+
+	stdout, stderr := s.RunMain(1, "gobco", "-verbose", "testdata/testmaintest")
+
+	s.CheckContains(stdout, "[build failed]")
+	s.CheckContains(stderr, ": undefined: gobcoCounts")
+}
+
 func Test_gobcoMain__oddeven(t *testing.T) {
 	s := NewSuite(t)
 	defer s.TearDownTest()

testdata/testmaintest/add.go

@@ -0,0 +1,5 @@
+package add
+
+func Add(x, y int) int {
+	return x + y
+}

testdata/testmaintest/add_test.go

@@ -0,0 +1,21 @@
+package add_test
+
+import (
+	add "github.com/rillig/gobco/testdata/testmaintest"
+	"os"
+	"testing"
+)
+
+// The TestMain function is defined in a black box test, thus the suffix
+// '_test' in the package name.
+
+func TestMain(m *testing.M) {
+	os.Exit(m.Run())
+}
+
+func TestAdd(t *testing.T) {
+	have, want := add.Add(1, 2), 3
+	if have != want {
+		t.Errorf("want %d, have %d", want, have)
+	}
+}