misc/cgo/test: test C.enum_*

Allocate a C enum object, and test if it can be assigned a value
successfully.

For #39537

Change-Id: I7b5482112486440b9d99f2ee4051328d87f45dca
GitHub-Last-Rev: 81890f40ac
GitHub-Pull-Request: golang/go#39977
Reviewed-on: https://go-review.googlesource.com/c/go/+/240697
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>

misc/cgo/test/cgo_test.go

@@ -76,6 +76,8 @@ func TestCheckConst(t *testing.T)            { testCheckConst(t) }
 func TestConst(t *testing.T)                 { testConst(t) }
 func TestCthread(t *testing.T)               { testCthread(t) }
 func TestEnum(t *testing.T)                  { testEnum(t) }
+func TestNamedEnum(t *testing.T)             { testNamedEnum(t) }
+func TestCastToEnum(t *testing.T)            { testCastToEnum(t) }
 func TestErrno(t *testing.T)                 { testErrno(t) }
 func TestFpVar(t *testing.T)                 { testFpVar(t) }
 func TestHelpers(t *testing.T)               { testHelpers(t) }

misc/cgo/test/test.go

@@ -1000,6 +1000,32 @@ func testEnum(t *testing.T) {
 	}
 }
 
+func testNamedEnum(t *testing.T) {
+	e := new(C.enum_E)
+
+	*e = C.Enum1
+	if *e != 1 {
+		t.Error("bad enum", C.Enum1)
+	}
+
+	*e = C.Enum2
+	if *e != 2 {
+		t.Error("bad enum", C.Enum2)
+	}
+}
+
+func testCastToEnum(t *testing.T) {
+	e := C.enum_E(C.Enum1)
+	if e != 1 {
+		t.Error("bad enum", C.Enum1)
+	}
+
+	e = C.enum_E(C.Enum2)
+	if e != 2 {
+		t.Error("bad enum", C.Enum2)
+	}
+}
+
 func testAtol(t *testing.T) {
 	l := Atol("123")
 	if l != 123 {