lang: Add a named error for catching errors in test on Init

This makes it so that we can catch errors that happen in Init. We also
name the errors so that number sequence doesn't matter.

lang/interpret_test.go

@@ -547,6 +547,7 @@ func TestAstFunc0(t *testing.T) {
 func TestAstFunc1(t *testing.T) {
 	const magicError = "# err: "
 	const magicError1 = "err1: "
+	const magicErrorFailInit = "errInit: "
 	const magicError2 = "err2: "
 	const magicError3 = "err3: "
 	const magicError4 = "err4: "
@@ -579,6 +580,7 @@ func TestAstFunc1(t *testing.T) {
 
 	type errs struct {
 		fail1    bool
+		failInit bool
 		fail2    bool
 		fail3    bool
 		fail4    bool
@@ -635,6 +637,7 @@ func TestAstFunc1(t *testing.T) {
 		// if the graph file has a magic error string, it's a failure
 		errStr := ""
 		fail1 := false
+		failInit := false
 		fail2 := false
 		fail3 := false
 		fail4 := false
@@ -647,6 +650,11 @@ func TestAstFunc1(t *testing.T) {
 				str = errStr
 				fail1 = true
 			}
+			if strings.HasPrefix(str, magicErrorFailInit) {
+				errStr = strings.TrimPrefix(str, magicErrorFailInit)
+				str = errStr
+				failInit = true
+			}
 			if strings.HasPrefix(str, magicError2) {
 				errStr = strings.TrimPrefix(str, magicError2)
 				str = errStr
@@ -672,6 +680,7 @@ func TestAstFunc1(t *testing.T) {
 			expstr: str,
 			errs: errs{
 				fail1:    fail1,
+				failInit: failInit,
 				fail2:    fail2,
 				fail3:    fail3,
 				fail4:    fail4,
@@ -709,6 +718,7 @@ func TestAstFunc1(t *testing.T) {
 			name, path, fail, expstr, errs := tc.name, tc.path, tc.fail, strings.Trim(tc.expstr, "\n"), tc.errs
 			src := dir + path // location of the test
 			fail1 := errs.fail1
+			failInit := errs.failInit
 			fail2 := errs.fail2
 			fail3 := errs.fail3
 			fail4 := errs.fail4
@@ -818,11 +828,27 @@ func TestAstFunc1(t *testing.T) {
 				},
 			}
 			// some of this might happen *after* interpolate in SetScope or Unify...
-			if err := ast.Init(data); err != nil {
+			err = ast.Init(data)
+			if (!fail || !failInit) && err != nil {
 				t.Errorf("test #%d: FAIL", index)
 				t.Errorf("test #%d: could not init and validate AST: %+v", index, err)
 				return
 			}
+			if failInit && err != nil {
+				s := err.Error() // convert to string
+				if s != expstr {
+					t.Errorf("test #%d: FAIL", index)
+					t.Errorf("test #%d: expected different error", index)
+					t.Logf("test #%d: err: %s", index, s)
+					t.Logf("test #%d: exp: %s", index, expstr)
+				}
+				return
+			}
+			if failInit && err == nil {
+				t.Errorf("test #%d: FAIL", index)
+				t.Errorf("test #%d: functions passed, expected fail", index)
+				return
+			}
 
 			iast, err := ast.Interpolate()
 			if err != nil {