test(sidekick): add test for codec helpers (#1587)

`language.Generate()` and `language.WalkTemplatesDir` are helpers for
the language codecs. They need unit tests, even though the integration
tests already use the code and indirectly test it.

Author: coryan

internal/sidekick/internal/language/generate_test.go

@@ -0,0 +1,56 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package language
+
+import (
+	"embed"
+	"os"
+	"path"
+	"testing"
+
+	"github.com/googleapis/librarian/internal/sidekick/internal/api"
+)
+
+//go:embed all:testTemplates
+var templates embed.FS
+
+func TestGenerate(t *testing.T) {
+	model := api.NewTestAPI([]*api.Message{}, []*api.Enum{}, []*api.Service{})
+	outDir := t.TempDir()
+
+	provider := func(name string) (string, error) {
+		contents, err := templates.ReadFile(name)
+		if err != nil {
+			return "", err
+		}
+		return string(contents), nil
+	}
+	// The list of files to generate, just load them from the embedded templates.
+	generatedFiles := WalkTemplatesDir(templates, "testTemplates")
+	err := GenerateFromModel(outDir, model, provider, generatedFiles)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, expected := range []string{"README.md", "test001.txt"} {
+		filename := path.Join(outDir, expected)
+		stat, err := os.Stat(filename)
+		if os.IsNotExist(err) {
+			t.Errorf("missing %s: %s", filename, err)
+		}
+		if stat.Mode().Perm()|0666 != 0666 {
+			t.Errorf("generated files should not be executable %s: %o", filename, stat.Mode())
+		}
+	}
+}

internal/sidekick/internal/language/testTemplates/README.md.mustache

@@ -0,0 +1,22 @@
+{{!
+Copyright 2025 Google LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+}}
+# Test Only - {{{Title}}}
+
+<!-- Code generated by sidekick. DO NOT EDIT. -->
+{{#Description}}
+
+{{{.}}}
+{{/Description}}

internal/sidekick/internal/language/testTemplates/common/partial.mustache

@@ -0,0 +1,17 @@
+{{!
+Copyright 2025 Google LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+}}
+
+{{! Verify partials are not included in Walk}}

internal/sidekick/internal/language/testTemplates/test001.txt.mustache

@@ -0,0 +1,16 @@
+{{!
+Copyright 2025 Google LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+}}
+{{>/testTemplates/common/partial}}

internal/sidekick/internal/language/walk_templates_dir_test.go

@@ -0,0 +1,39 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package language
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestWalkDir(t *testing.T) {
+	// It should get the `*.md.mustache` files and skip `partial.mustache`
+	got := WalkTemplatesDir(templates, "testTemplates")
+	want := []GeneratedFile{
+		{
+			TemplatePath: "testTemplates/README.md.mustache",
+			OutputPath:   "/README.md",
+		},
+		{
+			TemplatePath: "testTemplates/test001.txt.mustache",
+			OutputPath:   "/test001.txt",
+		},
+	}
+	if diff := cmp.Diff(want, got); len(diff) != 0 {
+		t.Errorf("mismatched config from LoadConfig (-want, +got):\n%s", diff)
+	}
+}