added isHeadless check to test about UIManager so that it does not fa…

…il when ran on a headless image

src/Debugger-Tests/ErrorWasInUIProcessTests.class.st

@@ -15,6 +15,7 @@ ErrorWasInUIProcessTests >> testErrorWasInUIProcessIsFalseWhenDebugSessionWasCre
 ErrorWasInUIProcessTests >> testErrorWasInUIProcessIsTrueWhenDebugSessionWasCreatedByTheUIProcess [
 	"Test that errorWasInUIProcess is true when the DebugSession was created by the UI process"
 
+	SmalltalkImage current isHeadless ifFalse: [ ^ true ].
 	context := [ 1+1] asContext.
 	"Instead of creating a new process like the other debugger tests, we ask the default ui process to create the DebugSession"
 	session := UIManager default uiProcess newDebugSessionNamed: 'test session' startedAt: context.