I generally check old line on the reel spool before going fishing and check line on the spool just sitting at home before spooling up.  In fact I look for line damage or just that line deformity of just sitting under pressure at the place on the rod tip guide.  I strip line when I deem it necessary.

Anyway, I always have a line to fall back on that I find as reliable. It may not be the strongest, the most limp, the best casting distance, the least memory, nor the most abrasion resistant line, but it is the most consistent line from the beginning of the spool to the end of the spool.   That's why I like Silverthread Excalibur and make it my goto line.  I also use it as a basis to compare to any other lines I use.  Well actually I used to use Trilene XL and XT as my basis to compare lines, but I've converted ever since encountering Silverthread Excalibur.

To test, I take a piece of line and tie my knots to the end of some swivel clips.  It's faster and easier to slide and remove knots off the clips rather than trying to snip it off just a swivel.  I use same knot on both ends tied to separate clips and pull test on Berkley 35 lb digital scale.  Gives me good idea of what to expect as well as my knot tying proficiency.

I've gathered some line break data on an altered Trilene Knot that I tie. I basically wrap the line four times and pass the tag end back around loop twice instead of the once that the normal Trilene Knot call for. I've found that this gives me the most consistency in knot and giving me a greater than 80% probability of 100% knot strength. I didn't account for the few knot failure breaks, because they tested lower. However even then for this particular line the knot failure breaks have consistently tested higher than box labeled line strenth. I was looking for consistent high line break data that I'm able to achieve repetitively. The tested line always showed line strain throughout the line, telling me it's an official line break.  It will not be a good choice to attempt to pull a snagged line to break in real world application.  It will leave a weakened spot elsewhere on the line to be snapped when least expected.

Trilene Knot (Altered)
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Silverthread Excalibur .179 mm 4# line break 5# 12 oz.
Silverthread Excalibur .245 mm 6# line break 9# 11 oz.
Silverthread Excalibur .275 mm 8# line break 11# 4 oz.
Silverthread Excalibur .303 mm 10# line break 13# 9 oz.
Silverthread Excalibur .330 mm 12# line break 15# 8 oz.
Silverthread Excalibur .355 mm 14# line break 18# 4 oz.

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For another popular knot, the Palomar Knot I've always have trouble achieve 100% line strength. It's kind of wishy washy since on average I will get less than 30% of 100% line strength. In simplicity it's an overhand knot and a loop that yeilds to a high potential of line pinch. Something of which I cannot truly confirm, but its very consisten in line breaks on the knot or very close to knot. There are times I will just give up trying to obtain data on a 100% knot to acquire the line break strength. Still it tests above box labeled line strength.  Very few line will show any kind of line strain throughout the entire tested line.  Tells me the breaks have a very high probability of being a knot related break.  Also means that the line integrity will be protected for those real world application of fishing and snagging bottom.

Palomar Knot
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Silverthread Excalibur .179 mm 4# line break 5# 14 oz.
Silverthread Excalibur .245 mm 6# knot break 8# 2 oz.
Silverthread Excalibur .275 mm 8# knot break 10# 12 oz.
Silverthread Excalibur .303 mm 10# knot break 12# 6 oz.
Silverthread Excalibur .330 mm 12# line break 15# 6 oz.
Silverthread Excalibur .355 mm 14# knot break 17# 5 oz.

Individual results will vary as their knot tying proficiency will differ.  Still I'm content that the results of line strength is still there even after these lines have been shelved for years.  Each knot has a particular use for me.  It's just the matter of choosing the right knot for the right application.  As long as I'm getting over box labed line test, I'm content with the line.  On occassion if I'm not sure I trust my results, I will tie a simple overhand knot into middle of line and test the line strength.  It should give me about box lable line test.  If it's less than 80% of it, I replace with new line.  In real world application, sometimes I will get a lure doing the single overhand knot on my line, and I will just keep on fishing with it.

Single Overhand Knot
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Silverthread Excalibur .179 mm 4# knot break 4# 4 oz.
Silverthread Excalibur .245 mm 6# knot break 6# 12 oz.
Silverthread Excalibur .275 mm 8# knot break 8# 12 oz.
Silverthread Excalibur .303 mm 10# knot break 9# 14 oz.
Silverthread Excalibur .330 mm 12# knot break 13# 2 oz.
Silverthread Excalibur .355 mm 14# knot break 14# 15 oz.