Allow functional arguments for provider callbacks and message producers

[JP-Ellis]

📝 Summary

Allows to functions to be passed in to handle provider states and to produce messages.

Still outstanding at the time of writing this PR is fully updated documentation.

As part of these changes,

🚨 Breaking Changes

This is all within the pact.v3 module which is not yet stable. The breaking changes are as follows:

• Verifier.set_info has been removed. Its functionality has been split across two functions:

  • Verifier.__init__ which takes two arguments now: the provider name and the host against which to run the provider tests.
  • Verifier.add_transport which behaves as before but now needs to be called at least once before executing .verify()

• Verifier.set_state has been replaced by Verifier.state_handler. This more correctly reflects the intent of the method.

🔥 Motivation

Previously, if one wanted to have a function be called to set the provider in a specific state, the end-user implementing the test suite would need to write a minimal HTTP server to effectively wrap this function.

This capability is still present, but it is now possible to pass in a function directly. Pact Python internally handles the HTTP server wrapper so the end user need not worry about that.

Similarly, the message producer required a HTTP wrapper to trigger the message generation. This has been made automatic with the end-user only requiring to define a function to handle that.

🔨 Test Plan

All existing tests have been adapted to make use of this feature.

🔗 Related issues/PRs

• Resolves: Relay messages in Pact Python #749

[JP-Ellis]

@valkolovos Here's the PR I have been talking about. Keen to have you give it a go and tell me what you think 🚀

[codecov]

Codecov Report

Attention: Patch coverage is 75.15723% with 79 lines in your changes missing coverage. Please review.

Project coverage is 78%. Comparing base (3f35067) to head (038fcc3).
Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pact/v3/verifier.py	58%	64 Missing ⚠️
src/pact/v3/_server.py	89%	15 Missing ⚠️

Additional details and impacted files

@@         Coverage Diff          @@
##           main   #890    +/-   ##
====================================
+ Coverage    59%    78%   +18%     
====================================
  Files        30     31     +1     
  Lines      3373   3665   +292     
====================================
+ Hits       2023   2859   +836     
+ Misses     1350    806   -544     

Flag	Coverage Δ
examples	57% <64%> (-3%)	⬇️
tests	77% <75%> (?)

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