Add test to show existing behavior

tests/functional/filter/cram/filter-query-backtick-quoting.t

@@ -0,0 +1,27 @@
+Setup
+
+  $ source "$TESTDIR"/_setup.sh
+
+Create metadata file for testing.
+
+  $ cat >metadata.tsv <<~~
+  > strain	region name
+  > SEQ_1	A
+  > SEQ_2	A
+  > SEQ_3	B
+  > SEQ_4	
+  > ~~
+
+The 'region name' column should be query-able by backtick quoting.
+This does not currently work due to a bug.
+
+  $ ${AUGUR} filter \
+  >  --metadata metadata.tsv \
+  >  --query '(`region name` == "A")' \
+  >  --output-strains filtered_strains.txt > /dev/null
+  ERROR: Could not infer columns from the pandas query. If the query is valid, please specify columns using --query-columns.
+  [2]
+
+  $ sort filtered_strains.txt
+  sort: No such file or directory
+  [2]