add test for DBInterface.prepare

Author: chris-b1

test/runtests.jl

@@ -1910,11 +1910,24 @@ end
             @test LibPQ.num_rows(result) == 1
             @test LibPQ.column_name(result, 1) == "typname"
             @test LibPQ.column_number(result, "typname") == 1
-
             data = columntable(result)
-
             @test data[:typname][1] == "bool"
 
+            qstr = "SELECT \$1::double precision as foo, typname FROM pg_type WHERE oid = \$2"
+            stmt = DBInterface.prepare(conn, qstr)
+            result = DBInterface.execute(
+                conn,
+                qstr,
+                (1.0, 16);
+            )
+            @test result isa LibPQ.Result
+            @test status(result) == LibPQ.libpq_c.PGRES_TUPLES_OK
+            @test isopen(result)
+            @test LibPQ.num_columns(result) == 2
+            @test LibPQ.num_rows(result) == 1
+            @test LibPQ.column_name(result, 1) == "foo"
+            @test LibPQ.column_name(result, 2) == "typname"
+
             DBInterface.close!(result)
             @test !isopen(result)