(testsuite) Added helper functions

- assert_source_completions()
- is_bash_completion_installed_for()

This allows for cleaner invocation of tests in `lib/completions/'.  For
example, `completion/perldoc.exp' now just contains:

    assert_source_completions perldoc

Skeleton test files for a command can be generated with:

    $ ./generate <command>

test/completion/perldoc.exp

@@ -1,3 +1 @@
-if {[assert_bash_type perl]} {
-    source "lib/completions/perldoc.exp"
-}; # if
+assert_source_completions perldoc

test/generate

@@ -14,9 +14,7 @@ generate_test_completion() {
     #if [ ! -f "$path" ]; then
             # No, file doesn't exist; generate file
     cat <<EXPECT > "$path"
-if {[assert_bash_type $1]} {
-    source "lib/completions/$1.exp"
-}; # if
+assert_source_completions $1
 EXPECT
     #fi
 } # generate_test_completion()

test/lib/library.exp

@@ -451,6 +451,23 @@ proc assert_no_complete {{cmd} {test ""}} {
 }; # assert_no_complete()
 
 
+# Source/run file with additional tests if completion for the specified command
+# is installed in bash.
+# @param string $command  Command to check completion availability for.
+# @param string $file  (optional) File to source/run.  Default is
+#                      "lib/completions/$cmd.exp".
+proc assert_source_completions {command {file ""}} {
+    if {[is_bash_completion_installed_for $command]} {
+        if {[string length $file] == 0} {
+            set file "lib/completions/$command.exp"
+        }
+        source $file
+    } else {
+        untested $command
+    }
+}; # assert_source_completions()
+
+
 # Sort list.
 # `exec sort' is used instead of `lsort' to achieve exactly the
 #  same sort order as in bash.
@@ -534,6 +551,24 @@ proc init_tcl_bash_globals {} {
 }; # init_tcl_bash_globals()
 
 
+# Check whether completion is installed for the specified command by executing
+# `complete -p ...' in bash.
+# @param string $command  Command to check completion availability for.
+# @return boolean  True (1) if completion is installed, False (0) if not.
+proc is_bash_completion_installed_for {command} {
+    set test "$command should have completion installed in bash"
+    set cmd "complete -p $command &> /dev/null && echo -n 0 || echo -n 1"  
+    send "$cmd\r"
+    expect "$cmd\r\n"
+    expect {
+        -ex 0 { set result true }
+        -ex 1 { set result false }
+    }
+    expect "/@"
+    return $result
+}; # is_bash_completion_installed_for()
+
+
 # Detect if test suite is running under Cygwin/Windows
 proc is_cygwin {} {
     expr {[string first [string tolower [exec uname -s]] cygwin] >= 0}