docs: Fix bug that caused the word "Beta" to appear twice in doc-strings (langchain-ai#17704)

The current issue:
Several beta descriptions in the API Reference are duplicated. For
example:
`[Beta] Get a context value.[Beta] Get a context value.` for the
[ContextGet
class](https://api.python.langchain.com/en/latest/core_api_reference.html#module-langchain_core.beta)
description.

NOTE: I've tested it only with a new ut! I cannot build API Reference
locally :(
This PR related to langchain-ai#17615

Author: leo-gan

libs/core/langchain_core/_api/beta_decorator.py

@@ -206,10 +206,9 @@ def finalize(  # type: ignore
 
         old_doc = inspect.cleandoc(old_doc or "").strip("\n")
 
+        # old_doc can be None
         if not old_doc:
-            new_doc = "[*Beta*]"
-        else:
-            new_doc = f"[*Beta*]  {old_doc}"
+            old_doc = ""
 
         # Modify the docstring to include a beta notice.
         notes_header = "\nNotes\n-----"
@@ -218,7 +217,7 @@ def finalize(  # type: ignore
             addendum,
         ]
         details = " ".join([component.strip() for component in components if component])
-        new_doc += (
+        new_doc = (
             f"[*Beta*] {old_doc}\n"
             f"{notes_header if notes_header not in old_doc else ''}\n"
             f".. beta::\n"

libs/core/tests/unit_tests/_api/test_beta_decorator.py

@@ -112,7 +112,7 @@ def test_beta_function() -> None:
 
         doc = beta_function.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")
 
     assert not inspect.iscoroutinefunction(beta_function)
 
@@ -132,7 +132,7 @@ async def test_beta_async_function() -> None:
 
         doc = beta_function.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")
 
     assert inspect.iscoroutinefunction(beta_async_function)
 
@@ -152,7 +152,7 @@ def test_beta_method() -> None:
 
         doc = obj.beta_method.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")
 
     assert not inspect.iscoroutinefunction(obj.beta_method)
 
@@ -173,7 +173,7 @@ async def test_beta_async_method() -> None:
 
         doc = obj.beta_method.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")
 
     assert inspect.iscoroutinefunction(obj.beta_async_method)
 
@@ -192,7 +192,7 @@ def test_beta_classmethod() -> None:
 
         doc = ClassWithBetaMethods.beta_classmethod.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")
 
 
 def test_beta_staticmethod() -> None:
@@ -211,7 +211,7 @@ def test_beta_staticmethod() -> None:
         )
         doc = ClassWithBetaMethods.beta_staticmethod.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")
 
 
 def test_beta_property() -> None:
@@ -231,13 +231,12 @@ def test_beta_property() -> None:
         )
         doc = ClassWithBetaMethods.beta_property.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")
 
 
-def test_whole_class_deprecation() -> None:
-    """Test whole class deprecation."""
+def test_whole_class_beta() -> None:
+    """Test whole class beta status."""
 
-    # Test whole class deprecation
     @beta()
     class BetaClass:
         def __init__(self) -> None:
@@ -269,6 +268,73 @@ def beta_method(self) -> str:
         )
 
 
+def test_whole_class_inherited_beta() -> None:
+    """Test whole class beta status for inherited class.
+
+    The original version of beta decorator created duplicates with
+    '[*Beta*]'.
+    """
+
+    # Test whole class beta status
+    @beta()
+    class BetaClass:
+        @beta()
+        def beta_method(self) -> str:
+            """original doc"""
+            return "This is a beta method."
+
+    @beta()
+    class InheritedBetaClass(BetaClass):
+        @beta()
+        def beta_method(self) -> str:
+            """original doc"""
+            return "This is a beta method 2."
+
+    with warnings.catch_warnings(record=True) as warning_list:
+        warnings.simplefilter("always")
+
+        obj = BetaClass()
+        assert obj.beta_method() == "This is a beta method."
+
+        assert len(warning_list) == 2
+        warning = warning_list[0].message
+        assert str(warning) == (
+            "The class `BetaClass` is in beta. It is actively being worked on, so the "
+            "API may change."
+        )
+
+        warning = warning_list[1].message
+        assert str(warning) == (
+            "The function `beta_method` is in beta. It is actively being worked on, so "
+            "the API may change."
+        )
+
+    with warnings.catch_warnings(record=True) as warning_list:
+        warnings.simplefilter("always")
+
+        obj = InheritedBetaClass()
+        assert obj.beta_method() == "This is a beta method 2."
+
+        assert len(warning_list) == 2
+        warning = warning_list[0].message
+        assert str(warning) == (
+            "The class `InheritedBetaClass` is in beta. "
+            "It is actively being worked on, so the "
+            "API may change."
+        )
+
+        warning = warning_list[1].message
+        assert str(warning) == (
+            "The function `beta_method` is in beta. "
+            "It is actively being worked on, so "
+            "the API may change."
+        )
+
+        # if [*Beta*] was inserted only once:
+        if obj.__doc__ is not None:
+            assert obj.__doc__.count("[*Beta*]") == 1
+
+
 # Tests with pydantic models
 class MyModel(BaseModel):
     @beta()
@@ -292,4 +358,4 @@ def test_beta_method_pydantic() -> None:
 
         doc = obj.beta_method.__doc__
         assert isinstance(doc, str)
-        assert doc.startswith("[*Beta*]  original doc")
+        assert doc.startswith("[*Beta*] original doc")