NEW: Include a build that tests the lowest composer dependencies

This will ensure that our claim that this module works with any framework 4.x
version is tested.

Note that 4.0.0-4.0.4 has some issues with its own test suite so we are
using 4.0.5 to test this.

.travis.yml

@@ -23,15 +23,26 @@ matrix:
     - php: 7.1
       env:
         - PHPUNIT_TEST=framework
+# Test with lowest composer requirements (i.e. framework 4.0). Ensure that recipe version matches composer.json
+        - COMPOSER_ARG="--prefer-lowest"
+        - RECIPE_VERSION=^4.0.5
     - php: 7.2
       env:
         - PHPUNIT_TEST=framework
-    - php: 7.3
+        - RECIPE_VERSION=^4.6
+    - php: 7.4
       env:
         - PHPUNIT_TEST=framework
+        - RECIPE_VERSION=4.x-dev
+
+    - php: 7.4
+      env:
+        - PHPUNIT_TEST=postgresql
+        - PHPCS_TEST=1
     - php: 7.1
       env:
         - PHPUNIT_TEST=postgresql
+        - COMPOSER_ARG="--prefer-lowest"
         - PHPCS_TEST=1
 
 before_script:
@@ -43,8 +54,9 @@ before_script:
 
 # Install composer dependencies
   - composer validate
-  - composer require --no-update silverstripe/recipe-cms:4.3.x-dev
-  - composer install --prefer-source --no-interaction --no-progress --no-suggest --optimize-autoloader --verbose --profile
+# Recipe is needed to pull in versioned and other packages for running the framework tests
+  - if [[ $RECIPE_VERSION ]]; then composer require --no-update silverstripe/recipe-cms:$RECIPE_VERSION; fi
+  - composer update $COMPOSER_ARG --prefer-source --no-interaction --no-progress --no-suggest --optimize-autoloader --verbose --profile
   - if [[ $PHPCS_TEST ]]; then composer global require squizlabs/php_codesniffer:^3 --prefer-dist --no-interaction --no-progress --no-suggest -o; fi
 
 script:

composer.json

@@ -15,11 +15,15 @@
         }
     ],
     "require": {
-        "silverstripe/framework": "^4",
-        "silverstripe/vendor-plugin": "^1.0"
+        "silverstripe/framework": "^4.0.5",
+        "silverstripe/vendor-plugin": "^1.0",
+        "composer/installers": "^1.5"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.7"
+        "phpunit/phpunit": "^5.7.27",
+        "sminnee/phpunit-mock-objects": "^3.4.5",
+        "nikic/php-parser": "^3 || ^4",
+        "monolog/monolog": "~1.16"
     },
     "extra": {
         "branch-alias": {