Explain version bounds in tests

Author: sharkdp

crates/red_knot_python_semantic/resources/mdtest/annotations/literal_string.md

@@ -1,10 +1,5 @@
 # `LiteralString`
 
-```toml
-[environment]
-target-version = "3.11"
-```
-
 `LiteralString` represents a string that is either defined directly within the source code or is
 made up of such components.
 

crates/red_knot_python_semantic/resources/mdtest/annotations/never.md

@@ -1,10 +1,5 @@
 # NoReturn & Never
 
-```toml
-[environment]
-target-version = "3.11"
-```
-
 `NoReturn` is used to annotate the return type for functions that never return. `Never` is the
 bottom type, representing the empty set of Python objects. These two annotations can be used
 interchangeably.
@@ -52,7 +47,7 @@ def f():
 
 ## `typing.Never`
 
-`typing.Never` is only available in Python 3.11 and later:
+### Python 3.11
 
 ```toml
 [environment]
@@ -61,9 +56,22 @@ target-version = "3.11"
 
 ```py
 from typing import Never
+from typing import Never
 
-x: Never
+reveal_type(Never)  # revealed: typing.Never
+```
 
-def f():
-    reveal_type(x)  # revealed: Never
+### Python 3.10
+
+```toml
+[environment]
+target-version = "3.10"
+```
+
+```py
+# TODO: should raise a diagnostic
+from typing import Never
+
+# TODO: this should be Unknown
+reveal_type(Never)  # revealed: Never
 ```

crates/red_knot_python_semantic/resources/mdtest/exception/except_star.md

@@ -1,5 +1,7 @@
 # Except star
 
+`except*` is only available in Python 3.11 and later:
+
 ```toml
 [environment]
 target-version = "3.11"

crates/red_knot_python_semantic/resources/mdtest/narrow/issubclass.md

@@ -101,14 +101,15 @@ else:
 
 ### Handling of `None`
 
+`types.NoneType` is only available in Python 3.10 and later:
+
 ```toml
 [environment]
 target-version = "3.10"
 ```
 
 ```py
-# TODO: this error should ideally go away once we (1) understand `sys.version_info` branches,
-# and (2) set the target Python version for this test to 3.10.
+# TODO: this error should ideally go away once we understand `sys.version_info` branches.
 # error: [possibly-unbound-import] "Member `NoneType` of module `types` is possibly unbound"
 from types import NoneType
 

crates/red_knot_python_semantic/resources/mdtest/type_alias.md

@@ -1,5 +1,7 @@
 # Type aliases
 
+Type aliases are only available in Python 3.12 and later:
+
 ```toml
 [environment]
 target-version = "3.12"