TST: add tests for unique values filtering

2 jobs for unique_filters in 1 minute and 28 seconds (queued for 1 second)
Name Stage Failure
failed
validate Test
Checking out c03d30c9 as unique_filters...
Skipping Git submodules setup
Checking cache for default...
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$ eclint check "**/*.html" "**/*.js" "**/*.css" "**/*.yaml" "**/*.md"
test/test-formhandler-unique.html
66:58 ❌ unexpected trailing whitespace (EditorConfig trim_trailing_whitespace https://goo.gl/oo8iVb)
ERROR: Job failed: exit code 1