feat: Add models.py and prompt.py to adk/skills to use in skill toolset

Also redefined schemas in models.py to be pydantic.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 866270203

tests/unittests/skills/__init__.py

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+# Copyright 2026 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
+#
+#     http://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.

tests/unittests/skills/test_models.py

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+# Copyright 2026 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
+#
+#     http://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.
+
+"""Unit tests for skill models."""
+
+from google.adk.skills import models
+import pytest
+
+
+def test_frontmatter():
+  """Tests Frontmatter model."""
+  frontmatter = models.Frontmatter(
+      name="test-skill",
+      description="Test description",
+      license="Apache 2.0",
+      compatibility="test",
+      allowed_tools="test",
+      metadata={"key": "value"},
+  )
+  assert frontmatter.name == "test-skill"
+  assert frontmatter.description == "Test description"
+  assert frontmatter.license == "Apache 2.0"
+  assert frontmatter.compatibility == "test"
+  assert frontmatter.allowed_tools == "test"
+  assert frontmatter.metadata == {"key": "value"}
+
+
+def test_resources():
+  """Tests Resources model."""
+  resources = models.Resources(
+      references={"ref1": "ref content"},
+      assets={"asset1": "asset content"},
+      scripts={"script1": models.Script(src="print('hello')")},
+  )
+  assert resources.get_reference("ref1") == "ref content"
+  assert resources.get_asset("asset1") == "asset content"
+  assert resources.get_script("script1").src == "print('hello')"
+  assert resources.get_reference("ref2") is None
+  assert resources.get_asset("asset2") is None
+  assert resources.get_script("script2") is None
+  assert resources.list_references() == ["ref1"]
+  assert resources.list_assets() == ["asset1"]
+  assert resources.list_scripts() == ["script1"]
+
+
+def test_skill_properties():
+  """Tests Skill model."""
+  frontmatter = models.Frontmatter(
+      name="my-skill", description="my description"
+  )
+  skill = models.Skill(frontmatter=frontmatter, instructions="do this")
+  assert skill.name == "my-skill"
+  assert skill.description == "my description"
+
+
+def test_script_to_string():
+  """Tests Script model."""
+  script = models.Script(src="print('hello')")
+  assert str(script) == "print('hello')"

tests/unittests/skills/test_prompt.py

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+# Copyright 2026 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
+#
+#     http://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.
+
+"""Unit tests for prompt."""
+
+from google.adk.skills import models
+from google.adk.skills import prompt
+import pytest
+
+
+class TestPrompt:
+
+  def test_format_skills_as_xml(self):
+    skills = [
+        models.Frontmatter(name="skill1", description="desc1"),
+        models.Frontmatter(name="skill2", description="desc2"),
+    ]
+    xml = prompt.format_skills_as_xml(skills)
+
+    assert "<name>\nskill1\n</name>" in xml
+    assert "<description>\ndesc1\n</description>" in xml
+    assert "<location>" not in xml
+    assert "<name>\nskill2\n</name>" in xml
+    assert "<description>\ndesc2\n</description>" in xml
+    assert xml.startswith("<available_skills>")
+    assert xml.endswith("</available_skills>")
+
+  def test_format_skills_as_xml_empty(self):
+    xml = prompt.format_skills_as_xml([])
+    assert xml == "<available_skills>\n</available_skills>"
+
+  def test_format_skills_as_xml_escaping(self):
+    skills = [
+        models.Frontmatter(name="skill&name", description="desc<ription>"),
+    ]
+    xml = prompt.format_skills_as_xml(skills)
+    assert "skill&amp;name" in xml
+    assert "desc&lt;ription&gt;" in xml