Create a tiny test suite

tests/.gitignore

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+/output.actual
+/test

tests/Makefile

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+CFLAGS = -I../libastro
+
+run-test: test
+	./test > output.actual
+	diff -u output.expected output.actual
+
+test: test.o ../libastro/libastro.a
+	$(CC) $< ../libastro/libastro.a -lm -o $@
+
+test.o: test.c
+
+../libastro/libastro.a: .FORCE
+	make -C ../libastro
+
+.PHONY: .FORCE

tests/output.expected

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+Precession J2000 -> J2015
+RA  +0.0000000000000000 -> +0.0033543649473764
+Dec -0.0000000000000000 -> +0.0014575063671504
+RA  +1.0000000000000000 -> +1.0014450289313686
+Dec -1.0000000000000000 -> -0.9992134064184917
+RA  +2.0000000000000000 -> +5.1478363700948195
+Dec -2.0000000000000000 -> -1.1409819639181964
+RA  +3.0000000000000000 -> +6.1449758360061262
+Dec -3.0000000000000000 -> -0.1401493826857086
+RA  +4.0000000000000000 -> +0.8630426367929015
+Dec -4.0000000000000000 -> +0.8593574646184613
+RA  +5.0000000000000000 -> +4.9986250865903390
+Dec -5.0000000000000000 -> +1.2835978054231891
+RA  +6.0000000000000000 -> +6.0032362075042789
+Dec -6.0000000000000000 -> +0.2845854258344847

tests/test.c

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+#include "astro.h"
+
+int main() {
+     printf("Precession J2000 -> J2015\n");
+     double ra, pra;
+     double dec, pdec;
+     for (double i=0.0; i<7.0; i+=1.0) {
+          ra = pra = i;
+          dec = pdec = -i;
+          precess(J2000, J2015, &pra, &pdec);
+          printf("RA  %+.16f -> %+.16f\n", ra, pra);
+          printf("Dec %+.16f -> %+.16f\n", dec, pdec);
+     }
+     return 0;
+}