What is an overview of conditional Biblical promises for truth seekers that can be empirically tested in their lifetime?

Here are a few conditional promises I was able to find after spending some time searching:

1. The promise of faith, to those who pray and fast. And the promise of miracles, to those who have (enough) faith.

20 He said to them, “Because of your little faith. For truly, I say to you, if you have faith like a grain of mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move, and nothing will be impossible for you.” 21 But this kind never comes out except by prayer and fasting [Matthew 17:20-21, ESV]

2. The promise of faith, to those who hear the word of Christ (i.e. the preaching of the Gospel, and possibly the reading of Scripture).

17 So faith comes from hearing, and hearing through the word of Christ. [Romans 10:17, ESV]

3. The promise of the Holy Spirit, to those who ask.

9 And I tell you, ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you. 10 For everyone who asks receives, and the one who seeks finds, and to the one who knocks it will be opened. 11 What father among you, if his son asks for a fish, will instead of a fish give him a serpent; 12 or if he asks for an egg, will give him a scorpion? 13 If you then, who are evil, know how to give good gifts to your children, how much more will the heavenly Father give the Holy Spirit to those who ask him!” [Luke 11:9-12, ESV]

4. The promise of power, to those who receive the Holy Spirit.

8 But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.” [Acts 1:8, ESV]

5. The promise of some sort of ecstatic experience, through the Holy Spirit, as "rivers of living water", to those who believe in Jesus and are spiritually thirsty.

37 On the last day of the feast, the great day, Jesus stood up and cried out, “If anyone thirsts, let him come to me and drink. 38 Whoever believes in me, as the Scripture has said, ‘Out of his heart will flow rivers of living water.’” 39 Now this he said about the Spirit, whom those who believed in him were to receive, for as yet the Spirit had not been given, because Jesus was not yet glorified. [John 7:37-39, ESV]

6. The promise of the fruit of the Spirit (i.e. sanctification, victory over sin, a transformed life), presumably to those who have already received the Spirit (see other promises above).

22 But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, 23 gentleness, self-control; against such things there is no law. 24 And those who belong to Christ Jesus have crucified the flesh with its passions and desires. [Galatians 5:22-24, ESV]

17 Now the Lord is the Spirit, and where the Spirit of the Lord is, there is freedom. 18 And we all, with unveiled face, beholding the glory of the Lord, are being transformed into the same image from one degree of glory to another. For this comes from the Lord who is the Spirit. [2 Corinthians 3:17-18, ESV]

4 in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit. 5 For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit set their minds on the things of the Spirit. 6 For to set the mind on the flesh is death, but to set the mind on the Spirit is life and peace. 7 For the mind that is set on the flesh is hostile to God, for it does not submit to God's law; indeed, it cannot. 8 Those who are in the flesh cannot please God.

9 You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you. Anyone who does not have the Spirit of Christ does not belong to him. 10 But if Christ is in you, although the body is dead because of sin, the Spirit is life because of righteousness. 11 If the Spirit of him who raised Jesus from the dead dwells in you, he who raised Christ Jesus from the dead will also give life to your mortal bodies through his Spirit who dwells in you.

[Romans 8:4-11, ESV]

7. The promise of spiritual gifts, presumably to those who have already received the Spirit (see other promises above) and subject ultimately to the Spirit's will.

4 Now there are varieties of gifts, but the same Spirit; 5 and there are varieties of service, but the same Lord; 6 and there are varieties of activities, but it is the same God who empowers them all in everyone. 7 To each is given the manifestation of the Spirit for the common good. 8 For to one is given through the Spirit the utterance of wisdom, and to another the utterance of knowledge according to the same Spirit, 9 to another faith by the same Spirit, to another gifts of healing by the one Spirit, 10 to another the working of miracles, to another prophecy, to another the ability to distinguish between spirits, to another various kinds of tongues, to another the interpretation of tongues. 11 All these are empowered by one and the same Spirit, who apportions to each one individually as he wills. [1 Corinthians 12:4-11, ESV]

8. The promise of being visited by Jesus and the Father, to those who love and obey Jesus. (Although there is an air of mystery around the exact meaning of this "visitation", since no further details are provided in the text. See @NigelJ's answer for further thoughts on this promise.)

23 Jesus answered him, “If anyone loves me, he will keep my word, and my Father will love him, and we will come to him and make our home with him [John 14:23, ESV]

9. The promise of prolonged life, to those who honor their parents.

Children, obey your parents in the Lord, for this is right. 2 “Honor your father and mother” (this is the first commandment with a promise), 3 “that it may go well with you and that you may live long in the land.” [Ephesians 6:1-3, ESV]

10. The promise of wisdom, to those who ask for it in faith.

5 If any of you lacks wisdom, let him ask God, who gives generously to all without reproach, and it will be given him. 6 But let him ask in faith, with no doubting, for the one who doubts is like a wave of the sea that is driven and tossed by the wind. 7 For that person must not suppose that he will receive anything from the Lord; 8 he is a double-minded man, unstable in all his ways. [James 1:5-8, ESV]

11. The promise of divine direction, to those who do not lean on their own understanding and acknowledge the Lord in everything.

5 Trust in the Lord with all your heart,
and do not lean on your own understanding.
6 In all your ways acknowledge him,
and he will make straight your paths.
[Proverbs 3:5-6, ESV]

12. The promise of finding God, to those who seek Him with all their heart, through prayer.

11 For I know the plans I have for you, declares the Lord, plans for welfare and not for evil, to give you a future and a hope. 12 Then you will call upon me and come and pray to me, and I will hear you. 13 You will seek me and find me, when you seek me with all your heart. 14 I will be found by you, declares the Lord, and I will restore your fortunes and gather you from all the nations and all the places where I have driven you, declares the Lord, and I will bring you back to the place from which I sent you into exile. [Jeremiah 29:11-14, ESV]

13. The promise to do works similar and even greater than those that Jesus did, to those who believe in Him. Also, in the next verse, the promise of answers to prayers, to those who ask in the name of Jesus.

12 “Truly, truly, I say to you, whoever believes in me will also do the works that I do; and greater works than these will he do, because I am going to the Father. 13 Whatever you ask in my name, this I will do, that the Father may be glorified in the Son. 14 If you ask me anything in my name, I will do it. [John 14:12-14, ESV]

14. The promise of different kinds of signs, to those who believe.

17 And these signs will accompany those who believe: in my name they will cast out demons; they will speak in new tongues; 18 they will pick up serpents with their hands; and if they drink any deadly poison, it will not hurt them; they will lay their hands on the sick, and they will recover.” [Mark 16:17-18, ESV]

15. The promise of perfect peace, to those who focus their minds on the Lord and trust in Him.

3 You keep him in perfect peace
whose mind is stayed on you,
because he trusts in you. 4 Trust in the Lord forever,
for the Lord God is an everlasting rock
[Isaiah 26:3-4, ESV]

4 Rejoice in the Lord always; again I will say, rejoice. 5 Let your reasonableness be known to everyone. The Lord is at hand; 6 do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. 7 And the peace of God, which surpasses all understanding, will guard your hearts and your minds in Christ Jesus. [Philippians 4:4-7, ESV]

16. The promise of (1) being approached by God, (2) freedom from the influence of the devil and (3) exaltation, to those who draw near to God, resist the devil, purify their hearts and humble themselves before the Lord (with mourning and weeping, in repentance).

7 Submit yourselves therefore to God. Resist the devil, and he will flee from you. 8 Draw near to God, and he will draw near to you. Cleanse your hands, you sinners, and purify your hearts, you double-minded. 9 Be wretched and mourn and weep. Let your laughter be turned to mourning and your joy to gloom. 10 Humble yourselves before the Lord, and he will exalt you. [James 4:7-10, ESV]

17. The promise of special revelations by God, to those who call to Him (and presumably have a spiritual status comparable to that of Jeremiah).

2 “This is what the LORD says, He who made the earth, the LORD who formed it to create it, He whose name is the LORD: 3 ‘Call to Me and I will answer you, and I will tell you great and mighty things, which you do not know.’ [Jeremiah 33:1-3, NASB]

18. The promise of financial/material prosperity, to those who tithe. (Note: some may object to this promise by arguing that tithing no longer applies to Christians, but I'm including it anyways for completeness.)

10 Bring the full tithe into the storehouse, that there may be food in my house. And thereby put me to the test, says the Lord of hosts, if I will not open the windows of heaven for you and pour down for you a blessing until there is no more need. 11 I will rebuke the devourer for you, so that it will not destroy the fruits of your soil, and your vine in the field shall not fail to bear, says the Lord of hosts. 12 Then all nations will call you blessed, for you will be a land of delight, says the Lord of hosts. [Malachi 3:10-12, ESV]

19. The promise that the everlating life is a present possession.

Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life. - John 5:24

Although some believe the freedom from condemnation refers to a future (post death) time, the acquisition of life is present tense and the passing from death to life is experienced rather than propositional.

20. The promise that the faithful will share in the sufferings of Christ.

If the world hate you, ye know that it hated me before it hated you. If ye were of the world, the world would love his own: but because ye are not of the world, but I have chosen you out of the world, therefore the world hateth you. Remember the word that I said unto you, The servant is not greater than his lord. If they have persecuted me, they will also persecute you; if they have kept my saying, they will keep yours also. But all these things will they do unto you for my name's sake, because they know not him that sent me. - John 15:18-21

These things have I spoken unto you, that ye should not be offended. They shall put you out of the synagogues: yea, the time cometh, that whosoever killeth you will think that he doeth God service. And these things will they do unto you, because they have not known the Father, nor me. - John 16:1-3

I am not able, at the present time, to give an 'overview' but I can certainly provide one example of what is required.

Jesus Christ himself makes one such promise :

Jesus answered and said unto him, If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him. [John 14:23 KJV]

Jesus promises that if anyone - anyone - loves him (and nothing more) then the inevitable consequence will be that that person will 'keep my words'. It is conditional : but the only condition is love.

And, further (another following promise) : my Father will love that person. Inevitably. Predictably. As an unerring consequence.

And more - and this shall be empirically tested by the recipients 'in this lifetime' - 'we will come unto him and make our abode with him'.

Now the coming of the Father and of the Son to a person, in one Holy Spirit, to dwell within that person, to 'make an abode' - this is the greatest of all experiences possible.

What more could a person ever desire or long for or expect ? And if fulfilled, what greater, what more sublime, what more blissful experience can there be in all existence ?

And all guaranteed. Absolutely promised. Just for love - and for nothing else.

And what greater confirmation of truth can there possibly be, than that God himself, in the Person of the Father and in the Person of the Son - in one Divine Holy Spirit - should so experimentally, so intimately, so abundantly be powerfully present within the person themselves ?

I know a couple of conditional biblical promises that were tested and proven true by many people in the Bible, both before the time of Christ, during his time, and henceforth, to this very day. I also know that huge numbers of Christians in a wide variety of denominations have tested this out and proven it to be true. And it appears to be incredibly simple.

"Taste and sees that the Lord is good" (Psalm 34:8). And,
"Kiss the Son... Blessed are all they that put their trust in him" (Psalm 2:12).

The promise is discovery of the Lord being good, and of being blessed. But the condition is tasting, and putting their trust in the Son of God.

The writer of those Psalms wrote reams more about having done just that, and agreeing that the Lord is good and that they were blessed by putting their trust in him. And many other characters detailed in the Bible had the same testimony.

But it takes faith to reach out to the Son, to kiss him, spiritually speaking, to put one's trust in him. Until a person does that, they will never experience the reality of the promise.

In lay terms, sort of: "The proof of the pudding is in the eating".

The invitation is there - test out whether God is good, and whether the Son of God will bless you by "tasting" and "kissing" - spiritually speaking!