Fix line count mismatch logic

Signed-off-by: Simon Alling <alling.simon@gmail.com>

internal/test/test.go

@@ -97,13 +97,15 @@ func AssertGoldenStringWithCustomLineValidation(t TestingT, checkLine func(expec
 		actualLineCount := len(actualLines)
 		for i := 0; i < max(expectedLineCount, actualLineCount); i++ {
 			lineNumber := i + 1
-			actualLine, expectedLine := "", "" // We do this to prevent index-out-of-range errors if the number of lines doesn't match between the expected and the actual output.
-			if i < actualLineCount {
-				actualLine = actualLines[i]
-			}
-			if i < expectedLineCount {
-				expectedLine = expectedLines[i]
-			}
+			// We need to prevent index-out-of-range errors if the number of lines doesn't match between the expected and the actual output.
+			// But we cannot just use the empty string as a default value, because that's equivalent to downright ignoring trailing empty lines.
+			if lineNumber > expectedLineCount {
+				t.Errorf("Output should only have %d line(s), but has %d. Line %d is: %q", expectedLineCount, actualLineCount, lineNumber, actualLines[i])
+			} else if lineNumber > actualLineCount {
+				t.Errorf("Output should have %d line(s), but has only %d. Line %d should have been: %q", expectedLineCount, actualLineCount, lineNumber, expectedLines[i])
+			} else {
+				actualLine := actualLines[i]
+				expectedLine := expectedLines[i]
 				if isSpecialLine, err := checkLine(expectedLine, actualLine); isSpecialLine {
 					if err != nil {
 						t.Errorf("Unexpected content on line %d (%v): %s", lineNumber, err.Error(), actualLine)
@@ -114,6 +116,7 @@ func AssertGoldenStringWithCustomLineValidation(t TestingT, checkLine func(expec
 			}
 		}
 	}
+}
 
 func path(filename string) string {
 	if filepath.IsAbs(filename) {