vhdl-testbench-architecture-file-name

vhdl-testbench-architecture-file-name is a variable defined in `vhdl-mode.el'.
Its value is

("\\(.*\\) \\(.*\\)" . "\\1_\\2")

Documentation:
Specifies how the testbench architecture file name is obtained.
The architecture file name can be obtained by modifying the testbench entity
and/or architecture name (e.g. attaching or stripping off a substring). The
string that is matched against the regexp is the concatenation of the entity
and the architecture name separated by a space. This gives access to both
names (see default setting as example). Testbench files can be created in
a different directory by prepending a relative or absolute path to the file
name.

FROM REGEXP is a regular expression matching the original name:
".*" matches the entire string
"\(...\)" matches a substring
TO STRING specifies the string to be inserted as new name:
"\&" means substitute entire matched text
"\N" means substitute what matched the Nth "\(...\)"
Examples:
".*" "\&" inserts original string
".*" "\&_i" attaches "_i" to original string
"\(.*\)_[io]$" "\1" strips off "_i" or "_o" from original string
".*" "foo" inserts constant string "foo"
".*" "" inserts empty string

You can customize this variable.