Fix error equals

[albertteoh]

Which problem is this PR solving?

Fixes a broken test introduced by an upgrade of go version to 1.15, caused by a change in the time package, specifically in format.go:1437.

Short description of the changes

• Although the practice of asserting on error messages is debatable, the spirit of this PR is to respect the original intention of this test in making a strong assertion on the specific input value which causes the error. Further, the error message should be consistent between OSes, just not between go versions of course.
• Fixes the broken test, which does not expect a quoted value in the error message. Go 1.15 introduces a sensible change of quoting the values to more clearly identify what is being parsed.
• The fix involves modifying the test to accept either quoted (1.15) or unquoted values (1.14 or below) in a regex of the error message and hence, ensures compatibility between both versions.
• Alternatives considered:
  • Using strings.HasPrefix which is slightly simpler but slightly reduces the fidelity of the test, losing a comparison on the actual value.
  • Just assert.Error(t, err), which is the simplest yet loses the most fidelity from the original test assertion.

Tested with the following to ensure they pass:

# Using go 1.14
$ go clean -testcache
$ go test github.com/jaegertracing/jaeger/cmd/query/app

# Switch to go 1.15
$ go clean -testcache
$ go test github.com/jaegertracing/jaeger/cmd/query/app

[jpkrohling]

LGTM. Ideally, we'd start wrapping the constant parts of the messages into the variable parts, making it easy to compare with errors.Is. That said, your PR improves the code base and prepares it for 1.15.

[yurishkuro]

Personally, having been burnt by the changing stdlib error messages in the past, I now try to write tests that only check for a substring or a prefix of the error which is stable and comes from our code, such as cannot not parse minDuration.

[albertteoh]

Yup, I would agree with that. Or, alternatively, wrap the error into a custom error type and assert on the type rather than error string comparisons.