Add golden tests for create-message-template

Author: chreekat

CONTRIBUTING.md

@@ -69,6 +69,9 @@ Pull requests that make it easier to understand or navigate are very
 welcome. The main generator `site.hs` is formatted using
 [Ormolu](https://github.com/tweag/ormolu).
 
+Finally, if you want to work on the scaffolding tool, it has a simplistic test script at
+`test/create-message-template/test.sh`.
+
 ## Reference: The Anatomy of a Message
 
 The Haskell Message Index is generated from a collection of files on

test/create-message-template/golden1.expected.txt

@@ -0,0 +1,46 @@
+This tool helps you create the scaffolding for a new error message on the error-message-index.
+You can leave any of the text fields blank and fill them in by hand later.
+
+· Which tool's error code do you want to document?
+ 1) GHC
+ 2) GHCup
+ 3) Stack
+Input (Default = GHC): 
+· What is the numeric code that you want to document?
+For example, enter "01234" if you want to document GHC-01234.
+Input: 
+· What is the title of the error message?
+This is used as the title of the documentation page as well as in links to the page.
+Input: 
+· Give a short summary of the error message.
+This appears on the overview page that lists all the documented errors and warnings.
+Input: 
+· What is the severity of the diagnostic?
+ 1) Error
+ 2) Warning
+Input (Default = Error): 
+
+· Which version of the tool emitted the numeric code (not the message) for the first time?
+Note: For GHC this is most likely 9.6.1.
+Input: 
+· How many examples should be generated?
+Input: 
+· Give a name for example 1
+The name should not contain spaces and begin with a lowercase letter.
+Input: 
+· Give a name for example 2
+The name should not contain spaces and begin with a lowercase letter.
+Input: 
+· Creating scaffolding...
+·· Created file messages/GHC-101010/index.md with these contents:
+
+---
+title: My Title
+summary: My summary which has a few words
+severity: error
+introduced: 9.6.1
+---
+
+Insert your error message here.
+·· Creating blank example in directory messages/GHC-101010/stunning-example...
+·· Creating blank example in directory messages/GHC-101010/sublime-example...

test/create-message-template/golden1.input.txt

@@ -0,0 +1,9 @@
+
+101010
+My Title
+My summary which has a few words
+
+9.6.1
+2
+stunning-example
+sublime-example

test/create-message-template/test.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+set -Eeuo pipefail
+
+cd "$(dirname $0)"
+trap "rm -rf golden*.output.txt messages" EXIT
+
+result=true
+
+for input in golden*.input.txt; do
+    output="$(basename -s .input.txt "$input").output.txt"
+    golden="$(basename -s .input.txt "$input").expected.txt"
+    runghc ../../message-index/create-message-template.hs < "$input" > "$output"
+    if [ ! -e "$golden" ]; then
+        cp "$output" "$golden"
+        echo "$golden created."
+    else
+        if diff -u "$golden" "$output"
+        then 
+            echo "$golden ok."
+        else
+            result=false
+            echo "$golden failed."
+        fi
+    fi
+done
+
+$result