test_wps_parser.py fails with "=" in condition

[cairosanders]

Describe the bug
The input for the wps_parser takes a logical condition. If passed a condition with a "=" (==, <=, >=) in it, the test fails. Any other condition passes the test. When using the process (for example in the wps_parser_demo.ipyn) the process completes as expected with a "=" symbol in the condition.

To Reproduce
Steps to reproduce the behavior:

1. Go to tests/test_wps_parser.py
2. Replace the existing condition with a condition containing "<=" or ">=" etc.
3. Run the test
4. See failed test (400 server error)

Expected behavior
test_wps_parser.py should pass the test with conditions containing "="