travis: Assert default datadir isn't created, Run scripted diff only once

.travis.yml

@@ -43,9 +43,9 @@ install:
     - if [ -n "$PACKAGES" ]; then travis_retry sudo apt-get update; fi
     - if [ -n "$PACKAGES" ]; then travis_retry sudo apt-get install --no-install-recommends --no-upgrade -qq $PACKAGES; fi
 before_script:
-    - if [ "$TRAVIS_EVENT_TYPE" = "pull_request" ]; then contrib/devtools/commit-script-check.sh $TRAVIS_COMMIT_RANGE; fi
-    - unset CC; unset CXX
+    - if [ "$CHECK_DOC" = 1 -a "$TRAVIS_EVENT_TYPE" = "pull_request" ]; then contrib/devtools/commit-script-check.sh $TRAVIS_COMMIT_RANGE; fi
     - if [ "$CHECK_DOC" = 1 ]; then contrib/devtools/check-doc.py; fi
+    - unset CC; unset CXX
     - mkdir -p depends/SDKs depends/sdk-sources
     - if [ -n "$OSX_SDK" -a ! -f depends/sdk-sources/MacOSX${OSX_SDK}.sdk.tar.gz ]; then curl --location --fail $SDK_URL/MacOSX${OSX_SDK}.sdk.tar.gz -o depends/sdk-sources/MacOSX${OSX_SDK}.sdk.tar.gz; fi
     - if [ -n "$OSX_SDK" -a -f depends/sdk-sources/MacOSX${OSX_SDK}.sdk.tar.gz ]; then tar -C depends/SDKs -xf depends/sdk-sources/MacOSX${OSX_SDK}.sdk.tar.gz; fi
@@ -70,6 +70,7 @@ script:
     - if [ "$RUN_TESTS" = "true" ]; then travis_wait 30 make $MAKEJOBS check VERBOSE=1; fi
     - if [ "$TRAVIS_EVENT_TYPE" = "cron" ]; then extended="--extended --exclude pruning,dbcrash"; fi
     - if [ "$RUN_TESTS" = "true" ]; then test/functional/test_runner.py --coverage --quiet ${extended}; fi
+    - if [ -d ~/.bitcoin ]; then false; fi  # Make sure default datadir does not exist after tests
 after_script:
     - echo $TRAVIS_COMMIT_RANGE
     - echo $TRAVIS_COMMIT_LOG