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take [something] as gospel

Free dictionary:

To believe that something is absolutely true without any hesitation or reservations.

When we're growing up, we take what our parents tell us as gospel.

The beloved professor's opinions on the author are taken as gospel by his students.

no questions asked

An expression indicating that one will not be questioned or hassled
about something, typically as an incentive for sharing some
information or doing something that otherwise may be the subject of
suspicion, further inquiry, or punishment.

From Farlex Dictionary of Idioms

Should fit into your context with the inclusion of a comma;

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs, no questions asked."

So I know that there are already a bunch of answers but I'll give my two cents anyway. In my opinion a more natural way to phrase this might be to use "the benefit of the doubt".

To retain a favorable or at least neutral opinion of someone or something until the full information about the subject is available.

So the sentence would be written like this:

We've been working together for quite some time now and I never saw him make a mistake, so I'm giving him the benefit of the doubt

Another common expression is:

take (someone or something) for granted

To consider something as being innately or unfailingly true, correct, real, or available.

(The Free Dictionary)

What was the idiom for something that we take without a doubt?

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs ______."

English almost always considers context. It's important to refer to the management cycle for software bugs:

"Bug management includes the process of documenting, categorizing, assigning, reproducing, correcting and releasing the corrected code. Proposed changes to software – bugs as well as enhancement requests and even entire releases – are commonly tracked and managed using bug tracking systems or issue tracking systems.

The items added may be called defects, tickets, issues, or, following the agile development paradigm, stories and epics. Categories may be objective, subjective or a combination, such as version number, area of the software, severity and priority, as well as what type of issue it is, such as a feature request or a bug.".

There's a few things at play here. It comes from the procedure for bug reporting.

1. You believe that they found something, they don't cry wolf.




2. They would want you to confirm it, you wouldn't want to send the work out or hire another employee without double checking that they are correct.




3. You need to assign a priority. Just because someone you trust discovers something doesn't mean that you would drop everything and assemble everyone for a meeting.

So, quite simply, you are accepting the report. You are receiving a bug report from the person, and taking it to the next step; without blindly agreeing with them.

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs as generally accepted."

That means that they are usually correct, you've not seen a prior error.

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am subscribing to his bugs."

That means that if they say there is a bug you want to hear about it. He is credible.

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am triaging his bugs."

That means that when they say there is a bug it goes to you. You double check and categorize it.

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs as genuine."

That does mean that he is always right, but no one would think that he could never be wrong.

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs as accredited."

That means that the person is highly experienced, they double check their own work, they are particularly familiar with the work; and it would be most unexpected that they could make an error.

It is for you to decide how much you want to stake your career and credibility on their word. There's also the consideration of whether they are the senior person whom assigns you work or whether you are the senior person whom double checks their work.

To give an analogy, do you want to say:

• "You would go mountain climbing with them", or "You would go camping with them".




• "You would let them pack the parachutes and fly the plane", or "You pack your own parachute, but enjoy jumping with them".

You want to avoid saying that they could never make any mistake and what they say is always of the most highest priority, they are not a religious leader or feared dictator. Even people here with the highest reputation have received downvotes.

I agree with user Jbro, the literal translation of your literal translation: "I am taking his words as a clean coin." is: His word is good as gold. That is an expression, actual gold would be more valuable unless he is a financial advisor or your software is mission critical.

How you say it reflects on both of you.

If you accept something without questioning it, you take it at face value.

To accept that something or someone is as it seems based only on an
initial or outward appearance, without further verifying or
investigating.

The source doesn't specify, but I assume this derives from accepting a coin as being worth the value stamped on its face without checking that it's authentic or that it hasn't been clipped of precious metal.

I'm taking his bugs as fact.

Just adding to the list. [I wish I could agree with myself.]

In the case of the bugs, I assume it'a situation where he says something like, "these are the problems I've found". You might answer, "ok, I'll take those findings on trust and won't double check."

Free dictionary definition:

take (something) on trust

To believe something implicitly, without requiring that someone
provide proof or evidence.
I took their explanation on trust, as
they've never given me reason before to disbelieve what they've told
me.
He wants us to take it on trust that he'll pay us back, but he
already owes us a substantial amount of money.

If it were directly his words you meant, you could say "I take his word for it". Or: "I'm taking him at his word."

[*Assuming your question was asked in good faith, it's not such a good idea to say what I did originally: "I'll take those bugs on trust and won't double check"...
and there's another sample answer: I'm traumatised and not going to take any more questions in good faith. It's usually used when you take something on trust with bad consequences.]

To take something as a given means to accept it without doubt - it is an infallible premise upon which you can work. A slightly more British form of this is to take something as given, which has the same meaning - it is something which does not need to be questioned or analyzed to accept its validity.

You can take that to the bank!

take-it-to-the-bank. Verb. (idiomatic) Said to emphasize that something is known for sure.
www.yourdictionary.com

Figurative: "What was said is the absolute truth and can be verified by a third party source." Comes from an obscure reference to cheques (or checks, if you're American), in that such is a guarantee that you can take the document to the bank and redeem it for its face value.
Urban Dictionary

As in:

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs whole schmear."

the whole schmear TFD an idiom

every aspect of something

Another phrase is "trust implicitly"

: being without doubt or reserve : UNQUESTIONING
an implicit trust

https://www.merriam-webster.com/dictionary/implicit

There's actually loads of idioms used for that phrase...

"Without a shadow of doubt" is the most common and only one which includes the word "doubt"

i.e. "Without a shadow of doubt we will win the next game"

Many phrases make use of the word 'blind' meaning the subject has more confidence than they can see, i.e. "Blind Faith" or "Follow x Blindly" means you have no doubt in whatever x is.

Also there are phrases that use the word 'Sure' like 'Sure as Shootin' (American specific) or 'It's a sure thing' meaning nothing can go wrong.

Other phrases include:

"All but won"
"(We got this) in the bag"
"(It's gonna be) a slam dunk"

But coming back to your original sentence, A couple of ways to make it work are:

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs blindly." probably the most accurate usage.

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs without a shadow of doubt."

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs as law."

"We've been working together for quite some time now and I never saw him make a mistake, henceforth I am taking his bugs on the chin."

^^ this last one is quite interesting and specific, but it would work in your example if you're trying to say "something might go wrong, but I don't care I'll be ready for it" so more about confidence than lack of doubt. It's a boxing metaphor so his bugs are like an opponent in the ring you're not scared of.

I am taking his words as axiomatic.

axiomatic ADJECTIVE

1 Self-evident or unquestionable.

‘it is axiomatic that dividends have to be financed’
Oxford Dictionaries

Surprised this hasn't been suggested yet:

“I am taking his words as read.”

Wiktionary describes this as ‘to assume that everyone agrees that something is correct’.

Collins describes is as to ‘accept it as true or right and therefore feel that it does not need to be discussed or proved’.

(It's also been discussed here before!)

I've been developing software for 25 years. I am adding this answer because, apart from the accepted "at face value" answer, almost everything suggested here sounds weird to me in context.

I'm taking his bug reports ____:

• as golden (might derive orginially from "good as gold" but that would sound awkward to me, like overselling it somehow. The phrase "golden master" refers to a final copy of software ready to ship, this may be where I get my bias for this.)




• without question (not really a slick, slang term like OP is asking for, but has some punch in this context because it's extremely unusual for us not to question you when you say there's something wrong with our code. Also in a comment on another answer here.)



• 
  as known quantities (plural feels weird here, I would say "I consider a bug report from him a known quantity").


• 
  as a sure thing (Might want to rephrase to singular as above). (Note that this is also in another response but buried with a lot of things that have a lot of context issues in my opinion)

Deservedly highly-upvoted here, but it struck me as having the nuance subtley off:

• "as gospel" (a bug report is a temporary truth, something you take "as gospel" would be like an opinion about a disputed coding practice or a statement about a particular standard). I might be too nit-picky here, it just felt like an oversell of what was trying to be expressed.

"slam dunk" has a similar "oversell" feeling to me, like, calm down a bit, it's just an accurate bug report, not a PhD.

To expand your vocabulary, another idiom for "genuine article" similar to your "clean coin" is real McCoy