Fix visualize tests

[JacobOaks]

PR #404 attempted to improve the tests in visualize_test.go by requiring length equality on the expected/actual ctors.

During CI, this actually uncovered a test failure:

--- FAIL: TestDotGraph (0.02s)
    --- FAIL: TestDotGraph/create_graph_with_one_constructor_and_as_interface_option (0.00s)
        visualize_test.go:453:
            	Error Trace:	visualize_test.go:453
            	            				visualize_test.go:117
            	Error:      	"[]" should have 1 item(s), but has 0
            	Test:       	TestDotGraph/create_graph_with_one_constructor_and_as_interface_option

This is because in this specific test case, the provide was never actually successful because of an error during provide (t5 did not implement io.Reader).

This commit:

• Changes all of the provides that are expected to pass to RequireProvide which will fail if the provide fails.
• Modifies t5 to implement io.Reader.
• Change the test case to expect the provider to only provide the interface in the fx.As (fx.As does not also provide the actual type)
• Add the len check from Improve visualize tests #404.

This supercedes #404.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (45369ac) 98.40% compared to head (dff4fbd) 98.40%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #405   +/-   ##
=======================================
  Coverage   98.40%   98.40%           
=======================================
  Files          22       22           
  Lines        1507     1507           
=======================================
  Hits         1483     1483           
  Misses         15       15           
  Partials        9        9           

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