Confusing when a got-away-with-it multiple snapshot stops getting away with it

[nedtwigg]

Story:

• a user has a test where they are taking multiple snapshots that have the same name
  • such as calling toMatchDisk() twice in one test
• the snapshots happen to be the same, so they get away with it
• something about the code being tested changes, and now the snapshots are different, so the test fails with this error message

• selfie/jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/guts/WriteTracker.kt

  Lines 70 to 94 in edb5f65

  	val howToFix =
  	when (this) {
  	is DiskWriteTracker ->
  	"You can fix this with `.toMatchDisk(String sub)` and pass a unique value for sub."
  	is InlineWriteTracker ->
  	"""
  	You can fix this by doing an `if` before the assertion to separate the cases, e.g.
  	if (isWindows) {
  	expectSelfie(underTest).toBe("C:\\")
  	} else {
  	expectSelfie(underTest).toBe("bash$")
  	}
  	"""
  	is ToBeFileWriteTracker ->
  	"You can fix this with `.toBeFile(String filename)` and pass a unique filename for each code path."
  	}
  	if (existing.snapshot != snapshot) {
  	throw layout.fs.assertFailed(
  	"Snapshot was set to multiple values!\n" +
  	" first value: ${existing.snapshot}\n" +
  	" this time: ${snapshot}\n" +
  	" first call: ${existing.callStack.ideLink(layout)}\n" +
  	" this call: ${call.ideLink(layout)}\n" +
  	"$howToFix",
  	existing.snapshot,

• The hotToFix is completely buried. It should come first!
• We should also advertise the allow_multiple_equivalent_writes_to_one_location property