add tests on reading actions registry from local file

scripts/generate-popular-actions/main.go

@@ -76,7 +76,7 @@ func newGen(stdout, stderr, dbgout io.Writer) *gen {
 func (g *gen) registry() ([]*registry, error) {
 	var a []*registry
 	if err := json.Unmarshal(g.rawRegistry, &a); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("could not parse the local action registry file as JSON: %w", err)
 	}
 	return a, nil
 }
@@ -291,7 +291,7 @@ func (g *gen) readJSONL(file string) (map[string]*actionlint.ActionMetadata, err
 		}
 		var j actionOutput
 		if err := json.Unmarshal(l, &j); err != nil {
-			return nil, fmt.Errorf("could not parse line as JSON for action metadata in file %s: %s", file, err)
+			return nil, fmt.Errorf("could not parse line as JSON for action metadata in file %s: %w", file, err)
 		}
 		ret[j.Spec] = j.Meta
 	}
@@ -432,7 +432,7 @@ Flags:`)
 	if registry != "" {
 		b, err := os.ReadFile(registry)
 		if err != nil {
-			fmt.Fprintf(g.stderr, "could not read actions registry from JSON file: %s\n", err)
+			fmt.Fprintf(g.stderr, "could not read the file for actions registry: %s\n", err)
 			return 1
 		}
 		g.rawRegistry = b

scripts/generate-popular-actions/main_test.go

@@ -292,8 +292,8 @@ func TestDetectNoRelease(t *testing.T) {
 				t.Fatal("exit status is non-zero:", status)
 			}
 			out := stdout.String()
-			if out != "" {
-				t.Fatalf("stdout is not empty: %q", out)
+			if out != "No new release was found\n" {
+				t.Fatalf("stdout is unexpected: %q", out)
 			}
 		})
 	}
@@ -373,11 +373,10 @@ func TestWriteError(t *testing.T) {
 }
 
 func TestCouldNotFetch(t *testing.T) {
-	stdout := testErrorWriter{}
 	stderr := &bytes.Buffer{}
 	f := filepath.Join("testdata", "registry", "repo_not_found.json")
 
-	status := newGen(stdout, stderr, io.Discard).run([]string{"test", "-r", f})
+	status := newGen(io.Discard, stderr, io.Discard).run([]string{"test", "-r", f})
 	if status == 0 {
 		t.Fatal("exit status is unexpectedly zero")
 	}
@@ -400,10 +399,9 @@ func TestInvalidCommandArgs(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(strings.Join(tc.args, " "), func(t *testing.T) {
-			stdout := testErrorWriter{}
 			stderr := &bytes.Buffer{}
 
-			status := newGen(stdout, stderr, io.Discard).run(tc.args)
+			status := newGen(io.Discard, stderr, io.Discard).run(tc.args)
 			if status == 0 {
 				t.Fatal("exit status is unexpectedly zero")
 			}
@@ -430,6 +428,38 @@ func TestDetectErrorBadRequest(t *testing.T) {
 	}
 }
 
+func TestReadActionRegistryError(t *testing.T) {
+	tests := []struct {
+		file string
+		want string
+	} {
+		{
+			file: "broken.json",
+			want: "could not parse the local action registry file as JSON:",
+		},
+		{
+			file: "oops-this-file-doesnt-exist.json",
+			want: "could not read the file for actions registry:",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.file, func(t *testing.T) {
+			stdout := io.Discard
+			stderr := &bytes.Buffer{}
+			f := filepath.Join("testdata", "registry", tc.file)
+			status := newGen(stdout, stderr, io.Discard).run([]string{"test", "-d", "-r", f})
+			if status != 1 {
+				t.Fatal("exit status is not 1:", status)
+			}
+			out := stderr.String()
+			if !strings.Contains(out, tc.want) {
+				t.Fatalf("wanted %q in stderr: %q", tc.want, out)
+			}
+		})
+	}
+}
+
 func TestActionBuildRawURL(t *testing.T) {
 	a := &registry{Slug: "foo/bar"}
 	have := a.rawURL("v1")

scripts/generate-popular-actions/testdata/registry/broken.json

@@ -0,0 +1,5 @@
+[
+    {
+        "slug": "rhysd/action-setup-vim",
+        "tags": ["v0"],
+        "next": "v1"