The plaintiffs have by affidavit shown that the defendants executed a note to plaintiffs and $2,300.00 is due on the note. The note was incorporated into the complaint and was considered by the court in determining the motion for summary judgment. The only part of the plaintiffs’ evidence that depends on the credibility of the plaintiffs as witnesses is the plaintiffs’ statement that *583the note was executed and the payments that were made by the defendants. The plaintiffs’ testimony by affidavit is not inherently incredible and is neither self-contradictory nor susceptible to conflicting inferences. The defendants have filed nothing which contradicts the evidence of the plaintiffs but have filed an affidavit which alleges they have a claim against the plaintiffs for work unperformed on a home sold by the plaintiffs to defendants. If the defendants are not able to set off this claim against the plaintiffs in this action, the plaintiffs are entitled to judgment as a matter of law. See Kidd v. Early, 289 N.C. 343, 222 S.E. 2d 392 (1976). We do not believe the defendants are entitled to set off their claim against the plaintiffs in this action. The claims of the parties against each other grew out of separate transactions. The defendants did not plead this claim against the plaintiffs and there being no dispute as to the claim of the plaintiffs against the defendants, summary judgment was proper. See Barber v. Edwards, 218 N.C. 731, 12 S.E. 2d 234 (1940).
The defendants also assign error to the court’s denial of their motion to amend their answer to assert a counterclaim. G.S. 1A-1, Rule 15, provides that 30 days after a pleading has been filed which does not require a responsive pleading, the pleading may be amended only by leave of the court. We hold the court did not abuse its discretion in this case. We note that the counterclaim which the defendants attempted to assert was not a compulsory counterclaim within the meaning of G.S. 1A-1, Rule 13(a). See Apartments, Inc. v. Landrum, 45 N.C. App. 490, 263 S.E. 2d 323 (1980).