CASE statements don't include the `CASE` and `END` keywords

[young-mmfm]

Mammoth seems to omit the CASE and END keywords:

mammoth/workspaces/mammoth/src/__tests__/select.test.ts

Line 893 in 8122afe

"text": "SELECT foo.id, (WHEN foo.value > $1 THEN $2 ELSE $3) greatness FROM foo",

When I run the query

"SELECT foo.id, (WHEN foo.value > $1 THEN $2 ELSE $3) greatness FROM foo"

Postgres returns:

ERROR:  syntax error at or near "WHEN"

When I run the query

"SELECT foo.id, (CASE WHEN foo.value > $1 THEN $2 ELSE $3 END) greatness FROM foo"

Postgres runs the query correctly.