Resolving this would be easier with more clear reproduction steps (e.g., what was the exact code you tried it on, what exact commands did you run, what output did you get, etc.).

I'm trying to generate javascript test and running in a browser.

what was the exact code:
I use cryptography libraries (xts and xtea part of the https://godoc.org/golang.org/x/crypto)

what exact commands did I run:

1. Running test
   gopherjs test -v golang.org/x/crypto/xts golang.org/x/crypto/xtea
   Output:
   gopherjs: Source maps disabled. Install source-map-support module for nice stack traces. See https://github.com/gopherjs/gopherjs#gopherjs-run-gopherjs-test.
   === RUN TestXTS
   --- PASS: TestXTS (0.03s)
   === RUN TestShorterCiphertext
   --- PASS: TestShorterCiphertext (0.00s)
   PASS
   warning: system calls not available, see https://github.com/gopherjs/gopherjs/blob/master/doc/syscalls.md
   ok golang.org/x/crypto/xts 0.383s
   gopherjs: Source maps disabled. Install source-map-support module for nice stack traces. See https://github.com/gopherjs/gopherjs#gopherjs-run-gopherjs-test.
   === RUN TestBlocksize
   --- PASS: TestBlocksize (0.00s)
   === RUN TestCipherInit
   --- PASS: TestCipherInit (0.00s)
   === RUN TestInvalidKeySize
   --- PASS: TestInvalidKeySize (0.00s)
   === RUN TestEncodeDecode
   --- PASS: TestEncodeDecode (0.00s)
   === RUN TestCipherEncrypt
   --- PASS: TestCipherEncrypt (0.00s)
   === RUN TestCipherDecrypt
   --- PASS: TestCipherDecrypt (0.00s)
   PASS
   warning: system calls not available, see https://github.com/gopherjs/gopherjs/blob/master/doc/syscalls.md
   ok golang.org/x/crypto/xtea 0.387s

All tests are launched

2. Generate javascript test
   gopherjs test -v -c golang.org/x/crypto/xts golang.org/x/crypto/xtea
   Output:
   -rw-rw-r-- 1 css css 1948315 Feb 27 16:50 xts_test.js
   -rw-rw-r-- 1 css css 81423 Feb 27 16:50 xts_test.js.map

In this part, only xts_test.js is generated instead of xts_test.js and xtea_test.js and it does not contain all tests.

Result of xts_test.js in a browser:
PASS xts_test.js:8891

The gopherjs command mimics the CLI of the cmd/go command. In cmd/go, the -c flag can only be used on a single package a time. See:

$ go test -v golang.org/x/crypto/xts golang.org/x/crypto/xtea
=== RUN   TestXTS
--- PASS: TestXTS (0.00s)
=== RUN   TestShorterCiphertext
--- PASS: TestShorterCiphertext (0.00s)
PASS
ok  	golang.org/x/crypto/xts	0.007s
=== RUN   TestBlocksize
--- PASS: TestBlocksize (0.00s)
=== RUN   TestCipherInit
--- PASS: TestCipherInit (0.00s)
=== RUN   TestInvalidKeySize
--- PASS: TestInvalidKeySize (0.00s)
=== RUN   TestEncodeDecode
--- PASS: TestEncodeDecode (0.00s)
=== RUN   TestCipherEncrypt
--- PASS: TestCipherEncrypt (0.00s)
=== RUN   TestCipherDecrypt
--- PASS: TestCipherDecrypt (0.00s)
PASS
ok  	golang.org/x/crypto/xtea	0.008s
$ go test -v -c golang.org/x/crypto/xts golang.org/x/crypto/xtea
cannot use -c flag with multiple packages

You can just invoke gopherjs -c twice to get the results you want:

gopherjs test -v -c golang.org/x/crypto/xts
gopherjs test -v -c golang.org/x/crypto/xtea

This bug needs to be fixed by adding a "cannot use -c flag with multiple packages" error message when multiple packages are provided to gopherjs test -c.